Michael Schumacher celebrated a sixth Canadian Grand Prix victory in Montreal to seize the lead in the World Championship for the first time this season.

Ferrari's five-time world beater fended off a sustained if never threatening challenge from the Williams-BMW of brother Ralf to win by 0.7 seconds on the Circuit Gilles Villeneuve.

Colombia's Juan Pablo Montoya paid for spinning on the second lap to finish close behind in third in his Williams with Renault's Fernando Alonso fourth - the quartet separated by just 4.4 seconds.

But David Coulthard's dream of driver glory looks to be over for another year after he slipped 29 points behind Schumacher after retiring his McLaren 47 laps into the 70-lap race when lying sixth.

Schumacher's fourth victory of the season and 68th of his career took him three points clear of McLaren's Kimi Raikkonen who finished sixth despite starting from the pit-lane.

Brazil's Rubens Barrichello finished fifth in the other Ferrari with Mark Webber seventh for Jaguar and Olivier Panis collecting his first point of the season with eighth in the Toyota.

Coulthard had moved up from 11th at the start with a mix of overtaking and pit-stop strategy when the latest and probably decisive set-back to his championship hopes occurred.

The 32-year-old is still mathematically in the hunt but it will take monumental change of fortune for him to fight back and he could soon be forced to ride shot-gun for Raikkonen.

Jenson Button's return following his crash in Monaco ended soon after Coulthard's exit as his BAR developed a fault while Justin Wilson retired his Minardi a few laps from the end.

Rookie Ralph Firman's first outing on the part street circuit on the Ile Notre Dame in the St Lawrence Seaway ended when he parked his Jordan-Ford on the grass 21 laps into the race with team-mate Giancarlo Fisichella quickly joining him in retirement.

Montoya's hopes of following up his victory in Monaco two weeks ago with a back-to-back triumph suffered a self-inflicted blow when he spun at the end of the second lap and dropped three places to fifth.

The 27-year-old had worked his way back up to third by the time he pitted for the first time at the end of lap 19.

Montoya's mistake allowed Schumacher to move into second spot but he was unable to get close enough to threaten his younger brother despite getting the gap down to less than half-a-second.

Schumacher inherited the lead at the end of lap 20 when Ralf made his pit-stop then produced a rapid lap to crucially return to the circuit fractions ahead of the Williams after making his own stop one lap later.

The 34-year-old was back in front five laps later when Alonso came in for his first stop and this time it was his turn to have his brother's quicker car looming large in his rear view mirror for lap after lap.

The Williams driver, who had started on pole for the second race in succession, pursued the 'Red Shark' for 25 laps but never looked like being able to make an overtaking bid.

The race was decided at the next pit-stop window as Ralf went in on lap 46 with Michael darting in next time round and again just managing to come back out while his brother was negotiating the first chicane.

Schumacher again found himself second to Alonso but regained the advantage when the Spaniard made his final stop with 15 laps left.

The Swiss-based racer again had his brother just fractions behind though never remotely coming near to making a bold bid for the lead while Montoya also got on the tail of his team-mate.

Raikkonen had opted to start from the pit-lane rather than last place on the grid having botched up qualifying, but he had worked his way up to fifth by the time he made his pit-stop just past the mid-way point of the race.

The 23-year-old only just made it with the rubber canvass on his right rear wheel working loose - the same also happened to Renault's Jarno Trulli - and came within inches of hitting Barrichello's Ferrari.

Raikkonen's points finish keeps him in the title hunt while he awaits the new McLaren but the Williams duo could also have a major say in the destination of the drivers' crown if they maintain their new found competitiveness.

Local hero Jacques Villeneuve's season of frustration intensified when he was forced to retire just 17 laps into his home grand prix - and the 25th anniversary of his father, Gilles, victory on the track that was named after him following his death in Belgium in 1982.

The former world champion, who has been highly critical of his BAR-Honda's reliability has finished just three of the eight races, this latest set-back inevitably increasing speculation that he is on his way out of the team and possibly Formula One.

Schumacher, who now has 999 career points, said: "That's a good number. In Germany if you achieve a number like that you have to give a free drink to everyone.

"That was the ideal result. It was a tight and tough race and I wasn't able to push all the way through and drove the pace I needed to.

"We had just a bit more fuel and that's what got us the win. I opened the gap in the pit-stop windows."

He added: "It is important to be leading the championship in what I have always said will be a hard season with a tough fight to the end.

"I was pessimistic about our chances here before the race but this was the ideal result at the end of a very tough and tight race."

Schumacher's brother said he was never in with a chance of trying to overtake the Ferrari despite being just fractions of a second adrift for much of the 70-lap battle.

"I was never close enough to try and that's why I didn't," said Schumacher junior. "But it's eight points for me and the team, it was important that we scored points.

"The team has developed the car massively and it is starting to pay off but we are still a long, long way from where we need to be."

Asked if Schumacher could have tried to overtake, Williams technical director Patrick Head said: "I thought Ralf would have got bored sitting there for 40 laps."

Ferrari's technical director Ross Brawn hailed Schumacher's performance in winning for the fourth time this season despite a brake problem having started third on the grid.

"Michael did a very good job of controlling the race despite brake wear problems right from the early stages," said Brawn. "We breathed a sigh of relief when we got to the chequered flag. the strategy worked well but the deciding factor was the way Michael drove."

Raikkonen, who had led the championship for seven races, said: "The result is not a disaster at all and the gap to Michael is only three points with plenty more races to go.

"I started the race from the pit-lane but after 10 to 15 laps the team told me to save my brakes and not to push but if you don't push you don't gain places."

Team-mate David Coulthard was forced to retire with a gearbox problem and is now a massive 29 points behind Schumacher at the mid-way point of the 16-race season.

He said: "Obviously a non-finish is never good but that's the way it went today. I have the pace but I just need to qualify better. There is still a long way to go in the championship yet."