Rahal, whose third-place finish in the race was enough to end the season as the points leader, prevented a unique exchange of champions when he won the title by four points, as Mansell arrives from Formula One and Andretti heads for a European base. But the race was a triumph for Mansell's new team, run by Paul Newman and Carl Haas, and a grand occasion for the Andretti family.
Michael's father Mario, who won the Formula One drivers' championship in 1978 and was a team-mate of Mansell at Lotus, finished second behind his son and ahead of Rahal, Eddie Cheever and his nephew John Andretti. Michael led the 84-lap race from start to finish, beating his father by 4.72sec.
Michael Andretti's victory was his fifth of the season - the most by any of the drivers - his second in a row at Laguna Seca and the 27th of his IndyCar career. He said: 'Of course we're not going (to Formula One) as champion, but we gave it our best shot.'
Andretti, who was the 1991 IndyCar champion, will be the first American to drive in Formula One since Cheever in 1989. He will fill the position left by Berger's departure for Ferrari but his team-mate has yet to be decided as McLaren negotiate a replacement for Honda engines and Ayrton Senna makes up his mind where to go next year.
MONTEREY GRAND PRIX (Laguna Seca, Calif, 84 laps) Leading results (US unless stated): 1 M Andretti Lola-Ford Cosworth XB 1hr 51min 34.423sec (ave speed 99.996mph, 160.92 kph); 2 M Andretti Lola-Ford Cosworth XB +4.715; 3 B Rahal Lola-Chevrolet-A +1 lap; 4 E Cheever Lola-Ford Cosworth XB +1; 5 J Andretti Lola-Chevrolet-A +1; 6 R Boesel (Bra) Lola-Chevrolet-A +1. Leading final standings: 1 Rahal 196pts; 2 Michael Andretti 192; 3 A Unser Jnr 169; 4 E Fittipaldi (Bra) 151; 5 S Goodyear (Can) 108; 6 Mario Andretti 105.Reuse content