The rivalry intensified after the 1989 San Marino Grand Prix, where the two drivers had an agreement that neither would get in each other's way to the first corner ("cf." 1982 San Marino Grand Prix). At the start, Senna got away in the lead and Prost followed him through the first corner without getting in his way. Gerhard Berger's crash on lap four stopped the race. At the restart, Prost got away the better of the two but Senna forced his way past him at the first corner, breaking the pair's agreement at the start of the race, leaving Prost furious. Senna argued that it was the restart. Prost himself was angered by McLaren apparently favouring Senna because of Senna's better relationship with engine supplier Honda, so he announced in mid-season that he had signed to race for Ferrari the following season. Prost mentioned many times during 1989 that he believed his car was not as competitive as Senna's, and even that this was confirmed to him by the CEO of Honda when Prost traveled to Japan. The information was actually confirmed during the French GP press conference when Ron Dennis said that Prost's car was consistently using more fuel, but not getting more power, than Senna's engine.