ON THE SIDELINES : Senna’s Record: 133.73 M.P.H.

Defending Formula One champion Ayrton Senna of Brazil turned in a record lap in first-day qualifying for the Japanese Grand Prix, but teammate and chief rival Alain Prost was right on his tail.

Senna, who must win the last two races of the season if he is to retain his title, lapped the 3.64-mile Suzuka circuit at 131.730 m.p.h. in a McLaren-Honda, bettering the record of 131.007 set in 1987 by Gerhard Berger of Austria in a Ferrari.

Nigel Mansell of Britain, returning from a one-race suspension for reckless driving, was second in today’s standings with a lap of 130.270 m.p.h. in a Ferrari.

Prost, who holds a 76-60 points lead over Senna, was third-fastest at 129.925 m.p.h. Prost would clinch his third Formula One driving title if Senna is unable to win the Japanese race and the season-ending Australian Grand Prix.

The starting grid for Sunday’s race will be set after a second day of qualifying on Saturday.