Michael Schumacher escaped what was set to be a thrilling battle for victory in the Canadian Grand Prix when Juan Pablo Montoya's Williams broke down with 12 laps to go.

Montoya was closing in on the Ferrari after a fascinating tactical race when his BMW engine failed on the pit straight.

That guaranteed Schumacher his sixth victory in eight races this year and extended what was already a daunting world championship lead to 43 points - more than four clear wins.

David Coulthard drove an excellent race from eighth on the grid to finish second in the McLaren, holding off a tough challenge from Ferrari's Rubens Barrichello in the closing laps.

Montoya was on a two-stop strategy with Schumacher on a one-stop, and Williams had decided in advance to stop early if there was a safety-car period.

It was a debatable tactic - as it turned out, Montoya might have been better advised to stay out, but the engine failure made that conjecture irrelevant.

The safety car Williams had expected was deployed on lap 14 because the BAR of Jacques Villeneuve had broken down in a dangerous place.

The strategy was very tight after we knew Montoya was on a two-stop Michael Schumacher

Montoya lost relatively little ground with the stop, and rejoined in fifth.

That position became third a lap after the safety car pulled off at the start of lap 18 thanks to a brilliantly opportunistic piece of overtaking.

Montoya passed both his team-mate Ralf Schumacher and the McLaren of Kimi Raikkonen at the start of lap 19.

The Colombian took advantage of a mistake by Ralf when the German, chasing McLaren's Kimi Raikkonen, cut across the last corner.

That meant Schumacher had to back off to ensure he did not pass Raikkonen, who was right in front of him - drivers are not allowed to gain an advantage from cutting a chicane.

In the confusion, Montoya pulled alongside both men as they went past the pits and passed them into the first corner.

Schumacher celebrates his 59th win - and Ferrari's 150th

Montoya was then able to stay close enough to Michael Schumacher to regain the lead when the Ferrari made its stop on lap 38.

The Williams had to stop again for more fuel after 52 laps and he rejoined about eight seconds behind Schumacher.

He was closing on the Ferrari driver when his engine failed on lap 58, sealing the Italian team's 150th Grand Prix win.

Schumacher said: "The strategy was very tight after we knew Montoya was on a two-stop so I had to push until after his second stop so we would know he was behind me."

The safety car meant Barrichello could not take advantage of a two-stop strategy.

Schumacher let Barrichello through into second place behind Montoya at the first corner.

The Brazilian was on a two-stop strategy and, with a much lighter car than Montoya, swept past the Williams into the lead on the pit straight at the start of lap two.

Barrichello initially held station not far in front of Montoya but from lap eight began to pull away at around a second a lap.

But the safety car nullified his advantage and he dropped behind Coulthard as a result of his extra stop.

Raikkonen slowed towards the end but held on to fourth place, with Giancarlo Fisichella fifth for Jordan and Jarno Trulli sixth in the Benetton.

Watch a round-up of the race