1991 San Marino Grand Prix

With the team under new management having been sold by Cyril De Rouvre , Stefan Johansson was replaced at AGS by Formula One debutant Fabrizio Barbazza .

Apart from Pirro, those who failed to pre-qualify included Olivier Grouillard in the new British-built Fomet-1 chassis debuted by the Fondmetal team. Despite teething troubles which prevented him from progressing any further, Grouillard said he was happy with the new car. [ 1 ] Seventh was the other Lambo of Nicola Larini , and bottom of the time sheets was Pedro Chaves in the sole Coloni , who suffered a gearbox failure during the session. [ 1 ]

Ayrton Senna claimed his 55th pole position from Riccardo Patrese , Alain Prost , Nigel Mansell and Gerhard Berger .

The formation lap saw two dramatic incidents: Prost spun off the track at Rivazza Turn, followed by Berger, who was able to continue. However Prost stalled the engine and did not take the start.

At the lights, Patrese took the lead ahead of Senna, whilst Mansell, already slow off the line with gearbox problems, retired near the end of lap 1 after a collision with Martin Brundle . He was followed out by Nelson Piquet who spun off on lap 2, Aguri Suzuki who spun off on lap 3 behind the leaders and Jean Alesi who also spun off on lap 3 attempting a rather foolhardy pass on Stefano Modena .

In a strong lead, Patrese pitted for originally what appeared to be an early stop to slicks turned out to be more serious – a misfire with a faulty camshaft sensor. He restarted last before retiring for good 9 laps later.

Berger was catching Senna, lapping 1.5 seconds quicker than his teammate. The lead was soon down to 5 seconds, with Modena a superb third from Satoru Nakajima and the two Minardis of Pierluigi Martini and Gianni Morbidelli .

Both McLarens pitted for tyres with Senna maintaining his lead. Just after setting fastest lap, Berger was delayed in traffic, held up by the trio of Maurício Gugelmin , Julian Bailey and Thierry Boutsen . Bailey himself moved past Andrea de Cesaris into 6th, whilst Nakajima retired with transmission problems.