Rubens Barrichello took an emotional first win of the year in front of Ferrari's fanatical tifosi, heading home team-mate Michael Schumacher in the eighth 1-2 result of the Scuderia's season.
The race was anything but easy for Ferrari, however, as both drivers were left down the order after morning rain left the track damp but drying when the lights went out.
The conditions had the teams scratching their heads right up to the five-minutes-to-go deadline for tyre choice and, while most opted to fit their usual dry-weather rubber, others - most notably poleman Barrichello, David Coulthard and Felipe Massa - chose to remain on intermediates. The Scot realised his 'error' as soon as the field set off on its warm-up lap, ducking into the pits at the end of the 3.6mile tour to rethink his strategy. Barrichello and Massa, meanwhile, took to their places on the grid.
The Brazilian knew that, with conditions improving all the time, he would have to make use of his lighter fuel load to sprint away over the opening few laps, and made a good start to head the field down to the Rettifilio chicane for the first time. The getaway needed to be spot-on, for Fernando Alonso made his usual flier from row two, and quickly jumped past both Michael Schumacher and Juan Montoya.
Incredibly, there was no contact at the chicane, although a couple of cars, including Schumacher's took to the concrete beyond the kerbs. The German, having passed Montoya courtesy of his short-cut, slowed to allow the Colombian back through, but also found himself being passed by Kimi Raikkonen's McLaren. There was worse to come for the world champion, however, for, as the field funnelled into the Roggia chicane, he received the lightest of taps but, being on the damp side of the road, spun round. Antonio Pizzonia and Olivier Panis were also delayed in the incident, the Frenchman terminally, but Schumacher resumed in 15th place.
While Barrichello attempted to make his escape, those behind jostled to be in position to assume the lead when the Ferrari eventually peeled off. Jenson Button was the man on the move, passing Raikkonen at the Lesmos on lap two, before repeating the trick on Montoya a lap later. This left the Briton, who had started sixth, pursuing Alonso, but it was the Spaniard who claimed the lead - and before Barrichello pitted, as the conditions switched suddenly to favouring those on dry-weather tyres. Renault passed Ferrari at the Ascari curves immediately before Barrichello was due to pit.
Massa joined his fellow Brazilian in opting for a tyre change, but wasted the move almost immediately by running into the side of Giorgio Pantano two laps on, damaging the nose of the Sauber and requiring a second stop.
Schumacher, by this stage, was already making his recovery, having passed Coulthard - who started from the pit-lane - and Giancarlo Fisichella to break into the top ten, but still lay behind his team-mate after the Ferrari crew turned Barrichello around in double quick time with just a splash of fuel.
Alonso's term in the lead lasted just five laps before the Spaniard made his own stop, handing the lead to Button, who now had a Michelin train comprising Montoya, Raikkonen and Sato in close company. Christian Klien and Mark Webber had made good use of the early confusion to hold sixth and seventh for Jaguar, with Barrichello and Schumacher occupying the final top ten spots.