Mark Webber claimed a second Monaco Grand Prix victory in three years, but was forced to hold on over the final ten laps as a slow burner produced a tense finish.
The Australian, having inherited pole courtesy of Michael Schumacher's Barcelona penalty, made a rare good start to hold the advantage heading into Ste Devote, with Nico Rosberg and Lewis Hamilton - the latter complaining of a poor launch - slotting into second and third.
The top three were then clear of the chaos that erupted in their wake, as Romain Grosjean was destabilised by a brush with a fast-starting Fernando Alonso, and ended up squeezing Michael Schumacher against the outside barrier. While the German was able to continue - as was Massa - Grosjean's Lotus slewed across the track forcing some of those behind to take to the cut-through while leaving those on his outside with little room for manoeuvre.
Kamui Kobayashi was sent skyward as he hit the back of cars ahead of him, while Pastor Maldonado and Pedro de la Rosa were also ruled out of the contest, the Venezuelan nosed into the barriers and the Spaniard returning to the pits with his HRT's rear wing dragging behind him after contact between the two. Despite that, the safety car was only needed for a couple of laps, and Webber again timed the restart perfectly, keeping Rosberg behind him, as Hamilton again lagged and fell into the clutches of the two Ferraris.
The other McLaren wasn't faring any better, with Jenson Button having avoided contact with the aerial Kobayashi and dropped to 14th as he was forced to take the long route around the opening corner. That dropped the Briton behind not only Bruno Senna, Paul di Resta and Daniel Ricciardo, who had all started behind him, but also Heikki Kovalainen, whose good getaway allowed the Caterham to slot into 13th.
Unable to find a way past the Finn, Button's strategy of taking the harder compound tyres in the hope of running longer than the frontrunners and gaining positions was essentially scuppered - along with those of de la Rosa and, after a handful of laps, Vitaly Petrov, who retired with electrical gremlins.
Typical of Monaco, there was little in the way of overtaking in the early stages, even with the current breed of Pirellis having promoted action at the previous five races, leaving the pit-stops for the strategists to try and work their opportunities. Even then, however, the situation was complicated by varying weather forecasts, with different teams predicting rain, of varying degrees, arriving at different times. As a result, even though Toro Rosso stopped Jean-Eric Vergne for the soft compound tyres on lap 17, it was fully ten laps more before any of the frontrunners pulled the trigger, with Mercedes deciding to give Rosberg a new set of boots even though he was hanging on to Webber's tail.
With the rain threat appearing to have abated, albeit temporarily, Rosberg's stop kick-started the copycats, with Webber, Hamilton and Kimi Raikkonen in two laps later, and Alonso following next time around, having briefly assumed the lead. Red Bull managed to produce a good stop, returning Webber to the fray ahead of his erstwhile pursuers, but Hamilton, while not appearing to have a poor stop to compare with those in earlier races, found himself jumped by Alonso when the order settled down again.
Felipe Massa led for a single lap before his own stop promoted Sebastian Vettel to the front, but the German, having used his lack of a qualifying lap in Q3 to pick his tyres and opted for the harder of the two options, was in no mood to follow suit, remaining out front almost twice as long as his rivals and, lapping faster than those on new rubber, putting himself in with a shout of the podium. When he finally succumbed to the need for new rubber, on lap 45 as the last driver to stop, another rapid turnaround by the RBR crew allowed the world champion to rejoin in fourth, and with enough in hand to repel a now disgruntled Hamilton up the hill from Ste Devote.