Red Bull Racing's decision to stop Sebastian Vettel just once in the 69th Monaco Grand Prix paid dividends as the German, aided by a late red flag, claimed his fifth victory of the 2011 F1 world championship.
The German led from pole position, but appeared to have thrown away the chance of victory when the Red Bull Racing team made an uncharacteristically poor tyre change on lap 16. The slip-up, in which there was a significant delay before Vettel could rejoin, was enough to allow McLaren's Jenson Button to take over at the front of the field.
The Briton, running on a second set of Pirelli's new supersoft tyres, was quickly able to extend his advantage over second place, to the extent that he almost had a full pit-stop in hand over the world champion, but the arrival of the safety car on lap 34 - just after Button had made his second stop - negated his gains, and handed the lead back to Vettel. With Button needing to use the harder tyres, a third stop also allowed Fernando Alonso into second, but the top three closed up as their respective strategies set the race up for an intriguing finish.
Unfortunately, a multi-car accident, right in front of the leaders, triggered a second safety car and, with Vitaly Petrov needing medical attention, the red flag. Instead of calling the result there and then, however, the organisers allowed the final six laps to be run but, with the teams allowed to fit fresh tyres and repair any damage to their cars, the suspense was removed and Vettel pulled away to win.
The first 16 laps may have been standard fare at the front of the field but, further back, the mixed-up grid provoked more passing than was seen in last season's race. While Vettel sprinted away at the front, Button held off a fast-starting Alonso into Ste Devote, while Nico Rosberg vaulted up to fifth, behind Mark Webber. Michael Schumacher dropped to tenth off the line as his Mercedes appeared to lapse into anti-stall mode, but the German was in feisty mood, surprising Lewis Hamilton at the hairpin, having already hit the rear of the McLaren at turn one.
Vettel was 2.4secs in front at the end of the opening lap, and 3.2secs by the end of lap two, but Button began to peg the German's advantage and just over four seconds split the top two by the completion of ten laps. While Alonso, Webber, Rosberg, Felipe Massa, Pastor Maldonado and Petrov held station through to eighth, Hamilton seized the first opportunity to repass Schumacher, diving inside the seven-time champion at Ste Devote, the pair making brief contact as he went through. Three laps later, Rubens Barrichello also mugged his former team-mate, and Schumacher pitted for a new front wing at the end of the tour.
Massa then suffered front wing damage after clipping the back of Rosberg, but it wasn't enough to prevent the Brazilian from passing his rival at Tabac next time around, with Maldonado taking advantage of the Mercedes going off-line to slip through into sixth.
At the same time, Button became the first meaningful pit-stop, dropping to fourth as he took on another set of the supersoft tyres. Rosberg followed the Briton in, but attention quickly fell on the Red Bull pit, which swiftly reacted to McLaren's move. The confusion that followed, however, suggested that the stop was intended for Webber, rather than Vettel, and there was a notable delay as the crew scrambled for tyres, struggling to get the blankets off in their haste to turn the leader around. Webber followed his team-mate in on the same lap, and also lost time as he had to queue for his change, dropping to 14th in the process.
The hold-up, which may or may not have been precipitated by Red Bull's decision to change its pit-stop procedure after believing that Ferrari was on to it, was enough for Button to assume the lead, and the Briton made the most of being on the softer Pirellis while Vettel made do with the harder prime tyre. Button's first lap out front was McLaren's 10,000th since it joined the world championship, and he was soon lapping a second a lap quicker than his pursuers.