Formula One's resident rainmeister came close to pouring cold water on what had been a red-hot world championship battle at Indianapolis, romping to a sixth victory of the year and only being kept in title check by an equally bravura performance from Kimi Raikkonen.

Before the event, all the talk had been about whether Schumacher could overcome a disappointing qualifying session - which had left him seventh on the grid - and limit the potential damage that could have been caused to his hopes of a sixth world crown by, primarily Juan Montoya. In the end, however, the German was able to call on the help of his extra team-mates in the heavens, turning the race on its head and taking him to within a solitary point of erasing Juan Manuel Fangio's name from another page in the record books.

The first shower swept through Indianapolis as the pomp of a traditional US pre-race build-up got into full swing. By the time that the cars were unleashed on their warming-up lap, however, the track was dry once again - setting the tone for the remainder of the afternoon. The weather would prove critical, with the arrival of rain - and the severity of the storms - having the potential to wreck the respective strategies and hopes of the various Michelin and Bridgestone runners.

In one case, however, hopes were dashed even before the first precipitation of the race arrived....

Starting from fourth on the grid, Montoya found himself swamped as the lights went out and, with Rubens Barrichello directly ahead of him also making a tardy getaway, the Colombian found himself losing vital places to Schumacher and Raikkonen. The Finn, on the other, hand, made a cracking start, and led comfortably into the first corner, before pulling away from the pack, which now found itself bottled up behind third place starter Olivier Panis.

Surprisingly, the entire 20-car field made it through the opening sequence of corners unscathed, but Ralph Firman then blotted its copybook by running hard into the back of Jos Verstappen and breaking the nose of his Jordan. The Briton was thus the first pit caller of the afternoon, but it would not be long before the rest of the field was pondering a similar move.

The spots of rain had just begun to appear on visors when Montoya's afternoon went awry. Determined to make up places as quickly as possible lest Schumacher get away from him, the Colombian attempted to make an audacious pass on the second Ferrari of Barrichello going into turn two. Already up on the kerbs before he had to turn in, Montoya found himself squeezed by the Brazilian, but it was the Ferrari driver who came off worst, being sent spinning into the gravel, where he remained beached.

The incident cost Montoya a couple of places as he attempted to lose the new nose ornament he temporarily picked up, but things were about to get worse for the Williams driver.

That first shower was brief, but had the effect of shuffling the order as Panis opted to stop for wet weather rubber. The Frenchman had already been passed by Ralf Schumacher, who acted as hare for Montoya in the early pursuit of Raikkonen, and was under heavy pressure from the world champion, too, before deciding that he lacked the grip to fight for places. With the saturation level rising, however, the Renaults moved further apart, with Fernando Alonso getting the better of David Coulthard, and Jarno Trulli losing out to the recovering Montoya, although it was apparent that the Colombian's straight-line speed - effected by a skinny wing on his FW25 - was being blunted by the damp track.

The in-between conditions appeared to be affecting the Bridgestone runners more than their Michelin cousins, however, and Coulthard soon proved the point by sweeping past both Alonso and Michael Schumacher in one move heading onto the main straight. Montoya attempted to follow the Scot through, flying past Schumacher as though the Ferrari was standing still. It was at this moment, however, that the stewards decided to announce that they were investigating the Colombian for his part in Barrichello's demise.

During the wettest part of the shower, Raikkonen had extended his advantage over Schumacher Jr to almost four seconds but, as the conditions eased, the German reeled him back in. His pursuit was cut short, however, by the need to make his first stop for tyres and fuel, and the timing could not have been worse for either the Williams team or several others up and down the pit-lane.

Just as it appeared that the rain had blown over, another shower appeared - and with a vengeance. Schumacher returned to the track on grooved slicks, and so too did Coulthard and Montoya, who stopped together barely two laps later. Again, the fates were against JPM for, not only was he about to go on to the wrong rubber for the impending conditions, but his fuel rig jammed, requiring the team to switch to the back-up.

Raikkonen, Alonso and Michael Schumacher all also pitted for more 'slicks' as the clouds decided whether they would unleash the full force of the storm, but the German was the only one to return to the pits within a lap as the severity of the downpour became apparent. Fitting intermediates to the F2003-GA, the world champion lost track position, but remained confident that he would be able to make up ground easily as his rivals either chose to stay out and struggle or make another time-consuming stop. Montoya, meanwhile, took his drive-thru' penalty, knowing that he would be coming in again for wets very shortly.

Jenson Button, who had stopped at just the right point to make an informed choice on tyres, showed just how tricky the conditions were by spinning out of second place, allowing the Jaguar team to run 1-2 for a handful of laps. That moment of glory ended abruptly when one of the green cars embedded itself in the tyre barrier but, given his recent run of misfortune, it was a relief to see that it was not Justin Wilson, who nevertheless had to tip-toe around while the Bridgestone runners in his wake prevented him from assuming top spot.

Joining Webber on the sidelines at this point was Ralf Schumacher who, on dry rubber, lost control of his Williams and, with no traction on the wet grass, backed into the tyres with terminal consequences. Team-mate Montoya also went off the road and, on recovering to the tarmac, headed straight for the pits to take on full wets, Michelin's intermediates being of little use against their Bridgestone rivals.

And so it was the Button now led a grand prix for the first time, heading Heinz-Harald Frentzen - who had also survived on one stop only - in second place. Wilson, Raikkonen, Coulthard and Alonso were next up, ahead of the world champion, but the order continued to change with some rapidity as the conditions prompted teams to alter strategies and tyre choices.

Having made two stops for a change of rubber, and another to serve his penalty, Montoya then suffered the indignity of being lapped by the leading BAR with just 24 laps on the board. Although he was now on the closest thing he could be to the correct tyres, Montoya continued to lose time, leaving him to rely on a high rate of attrition if his title hopes were to linger on to Suzuka.

Schumacher lapped his great rival four laps later and, making up places with some regularity, appeared destined to take his sixth crown one race ahead of the Japanese denouement that everyone had been expecting. Raikkonen was despatched with shortly before passing the Williams and, with two other Bridgestone-shod cars - Button and Frentzen - between himself and first place, things didn't look too good for the Finn unless a dry line appeared to guide him back to Schumacher's shoulder.

The German duly passed Frentzen without too much opposition from his countryman - even when the Ferrari ran off line in the next corner - and was closing in on Button with some ease. Although the Briton made a slightly better job of appearing to defend his position, there was little resistance to prevent the champion-elect from assuming the lead.

Button's dream of a maiden podium then went up in smoke as his Honda engine expired, removing one obstacle from Raikkonen's path, but the question of relative fuel loads and when the opportunity to change back to slicks would arise lingered on. The race, it should be noted, was barely at half-distance....

Schumacher and Frentzen continued to head the field until lap 55, when Raikkonen, who had stopped for his return to 'slicks' just as Button retired, eventually passed the Sauber, having earlier leap-frogged Nick Heidfeld, who was adding to the Swiss team's good day. The Finn was, however, a long way from Schumacher, who continued serenely on, having briefly ceded the lead to HHF when he returned to dry weather tyres, only to regain the advantage when the Sauber driver followed suit.

Behind the top three, Heidfeld continued ahead of Jarno Trulli until the Italian put Michelin's dry weather tyres to good use in the closing stages, but was prevented from falling any further back by Montoya's woes. Having been lapped once, the Colombian briefly fell two laps behind the leader when he stopped to change back onto grooved tyres, but could do little about the Sauber, whom he trailed by a full tour even after using him to help drafted past Giancarlo Fisichella.

The Jordan driver had prayed before the race for rain and, with his wish coming true, used it to good effect by running in the points for the latter half of the race. Making just two stops where most of his rivals opted for three or four - or in some particular cases, five or six - the Italian could do little about the power of Montoya's BMW V10, but hung in there for seventh spot and two valuable points.

Fisichella also had the best part of a lap in hand on his nearest rival, such was the effect the weather had had, but an equally warm welcome was reserved for Wilson when he returned to the paddock with his first F1 point. The Briton had driven solidly all afternoon, making fewer mistakes than most as he got vital race distance mileage under his belt with the Jaguar.

Wilson had appeared to be under threat from the second BAR of Jacques Villeneuve, but the Canadian exited in a huge plume of white smoke ten laps from home, adding his name to those of Alonso (engine), Panis (accident), Coulthard (mechanical) and Firman (suspension) who had joined the list of retirements in the second half.

Other than a brief flurry when the weather gods toyed with the pit-lane for a third time, the remainder of the race passed with little incident, the field too spread out to provide the sort of close - if rather less contrived - finish that the American crowd had been 'treated' to last season.

Schumacher headed the field by fully 18secs as he laid one hand on the championship, but it was Raikkonen's progress that had caught the attention, as the pit-lane wondered whether McLaren was cutting it fine on fuel. Any further stop to 'splash and dash' would likely have dropped the Finn out of second spot, handing Schumacher the vital extra points he required to sew up the title one race early.

As it turned, Raikkonen, McLaren and Mercedes will get another - slim - chance to depose the German in two weeks' time. But, even though he may have shunned the one-arm bandits and roulette tables on a pre-race visit to Las Vegas, Schumacher must surely be tempted to lay a wager on that sixth crown now.

Race result:

1. Michael Schumacher Germany Ferrari-Ferrari 73 laps 1hr 33min 35.997secs
2. Kimi Raikkonen Finland McLaren-Mercedes +18.200secs
3. Heinz-Harald Frentzen Germany Sauber-Petronas +37.900secs
4. Jarno Trulli Italy Renault-Renault +48.300secs
5. Nick Heidfeld Germany Sauber-Petronas +56.400secs
6. Juan Montoya Colombia Williams-BMW +1 lap
7. Giancarlo Fisichella Italy Jordan-Ford +1 lap
8. Justin Wilson Britain Jaguar-Cosworth +2 laps

9. Cristiano da Matta Brazil Toyota-Toyota +2 laps
10. Jos Verstappen Holland Minardi-Cosworth +4 laps
11. Nicolas Kiesa Denmark Minardi-Cosworth +4 laps

Rtd Jacques Villeneuve Canada BAR-Honda 63 laps completed
Rtd Ralph Firman Britain Jordan-Ford 48 laps completed
Rtd David Coulthard Britain McLaren-Mercedes 45 laps completed
Rtd Fernando Alonso Spain Renault-Renault 44 laps completed
Rtd Jenson Button Britain BAR-Honda 41 laps completed
Rtd Olivier Panis France Toyota-Toyota 27 laps completed
Rtd Mark Webber Australia Jaguar-Cosworth 21 laps completed
Rtd Ralf Schumacher Germany Williams-BMW 21 laps completed
Rtd Rubens Barrichello Brazil Ferrari-Ferrari 2 laps completed

Fastest lap:

Michael Schumacher Ferrari-Ferrari 1min 11.473secs lap 13