Tension and mistrust between the two drivers increased when Senna overtook Prost at the restart of the San Marino Grand Prix, a move which Prost claimed violated a prerace agreement (Senna denied the existence of any agreement, though Prost's story was backed up by John Hogan of the team's major sponsor, Marlboro).
A tensión e a desconfianza entre os dous pilotos aumentou cando Senna superou a Prost na reanudación do Gran Premio de San Mariño, unha acción que segundo Prost violaba un acordo previo á carreira (Senna negou a existencia de calquera acordo, aínda que a historia de Prost foi apoiada por John Hogan, do principal patrocinador do equipo, Marlboro).