Senna had been running a strong second after a clumsy pit stop by the Williams-Renault crew left Damon Hill out of the equation. The Englishman had to sit for 17 seconds in his cockpit as the crew, not ready for him at the end of the 30th lap, rushed around to gather the four wheels and equip him with fresh rubber. Hill finished third, well down on Schumacher.
Second place would have been enough to keep Senna at the head of the drivers' standings, albeit by only one point, but now Prost has the advantage and, on the evidence of his performance and the pace of the Williams at the Circuit Gilles Villeneuve, it seems inevitable he will still be there at the end of the season.
Gerhard Berger brought the one surviving Ferrari home in fourth place and Britain's Martin Brundle fulfilled the promise of his weekend with fifth place in his Ligier-Renault.
Hill had the better of Prost into the first corner and led the way for five laps, the Williams pair confirming their superiority as the rest jostled for position in their wake. Senna, starting eighth on the grid, was away in magnificent style, taking Schumacher and then Ferrari's Jean Alesi in a breathtaking wheel-to- wheel dice.
Prost, always ominously close to Hill, made his move at the East Hairpin, ushering his car inside Hill's, and the Englishman had no real defence. Thereafter, the Frenchman's maiden victory on this circuit, his fourth of the season and his 48th in all, was scarcely in doubt. He had been in masterful form all weekend and the forthcoming tracks will surely suit this driver-car combination.
Prost said the race was not as easy at it looked. 'It may have looked easy but it wasn't. I really had to push hard and on the limit to stay in front.'
Hill then had a part to play for his partner and team, as well as for himself. As long as he contained Senna, Prost was assured his elevation to the top of the championship.
For all Senna's hustling, Hill managed to stay ahead of the Brazilian until that fateful pit stop. He said: 'I really don't know what happened at the pit stop, but I suppose you could say they weren't ready. They were all looking around for tyres. We lost a lot of time and simply couldn't make up the ground. Towards the end the engine didn't seem to be quite right so I thought it was better not to push too hard. It was vital to finish rather than break down.'
Schumacher, who said he had a problem at the start, demonstrated the speed he, too, had shown in practice and gradually brought Senna within his sights.
They were only half a second apart as Schumacher lined up his attack on the outside. It was a bold move and it appeared Senna was rather slower into the corner. The cars twitched as Schumacher ran almost on to the grass and he managed to squirm free. Senna, however, merely coasted to a halt, his race run and his tenuous hold on the championship lead gone.
Schumacher said: 'I like a good fight and I enjoyed my battle with Senna, but perhaps it was a little too close on this occasion. I was lucky to get through and lucky not to hit the wall. Maybe he didn't see me. He appeared to slow down as I was catching, so maybe he was just tired and wanted to stop for a rest.'
Senna explained: 'The car suddenly started cutting out and I was so concerned about it that I didn't see Schumacher coming on the outside. I am sorry that we touched.'
If it was a frustrating conclusion for Senna, it was another desperate day from the very start for his team-mate, Michael Andretti. The American, who had managed only two points from the first six races, was left stranded on the grid as the rest pulled away on their warm-up lap and he was pushed to the end of the pit lane. He eventually joined the action two laps into the race, all hope of adding points to his tally already dashed.
It was a disappointing afternoon, too, for Britain's Mark Blundell, who spun out after only 14 laps. However, his Ligier-Renault partner, Brundle, was equal to the task and underlined the consistency and competitiveness of his current form.
Johnny Herbert, who is having a less satisfying run in the Lotus-Ford, hung on for a creditable 10th and Derek Warwick struggled manfully to finish 16th in the Footwork-Mugen.
CANADIAN GRAND PRIX (Montreal, 69 laps, 305.670km): 1 A Prost (Fr) Williams-Renault 1hr 36min 41.822sec (ave speed 189.667kph); 2 M Schumacher (Ger) Benetton-Ford +14.527sec; 3 D Hill (GB) Williams-Renault +52.685; 4 G Berger (Aut) Ferrari +1 lap; 5 M Brundle (GB) Ligier-Renault +1; 6 K Wendlinger (Aut) Sauber +1; 7 J J Lehto (Fin) Sauber +1; 8 E Comas (Fr) Larrousse- Lamborghini +1; 9 C Fittipaldi (Bra) Minardi-Ford +2 laps; 10 J Herbert (GB) Lotus-Ford +2; 11 A Zanardi (It) Lotus-Ford +2; 12 T Boutsen (Bel) Jordan-Hart +2; 13 A Suzuki (Japan) Footwork- Mugen Honda +3; 14 M Andretti (US) McLaren- Ford +3; 15 L Badoer (It) Lola-Ferrari +4; 16 D Warwick (GB) Footwork-Mugen Honda +4; 17 U Katyama (Japan) Tyrrell-Yamaha +5; 18 A Senna (Bra) McLaren-Ford +7. Did not finish (not classified): 19 R Patrese (It) Benetton-Ford 52 laps; 20 A de Cesaris (It) Tyrrell-Yamaha 45; 21 F Barbazza (It) Minardi-Ford 33; 22 J Alesi (Fr) Ferrari 23; 23 M Blundell (GB) Ligier-Renault 13; 24 R Barrichello (Bra) Jordan-Hart 10; 25 P Alliot (Fr) Larrousse- Lamborghini 8. Fastest lap: Schumacher 1:21.500 (195.681 kph).
World Drivers' Championship standings (after seven rounds): 1 Prost 47pts; 2 Senna 42; 3 Hill 22; 4 Schumacher 20; 5 Brundle 7; 6= Blundell, Herbert; 8= Lehto, Patrese, Fittipaldi, Berger 5; 12 Alesi 4; 13= Alliot, Barbazza, Andretti 2; 16= Zanardi, Wendlinger 1. Constructors' championship: 1 Williams 69; 2 McLaren 44; 3 Benetton 25; 4 Ligier 13; 5 Ferrari 9; 6= Lotus, Minardi 7; 8 Sauber 6; 9 Larrousse 2.
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