Live coverage Sunday, BBC Two - 1230 GMT
Valentino Rossi set a new lap record at Valencia as he claimed pole for the final MotoGP of the season on Sunday.
Rossi (left) and Hayden (right) are going head-to-head for the title
Nicky Hayden, the only man who can deprive Rossi of a sixth world title, starts in fifth with Troy Bayliss second and Loris Capirossi in third.
Rossi, whose winning time was one minute 31.002 seconds, leads by eight points, after previous leader Hayden crashed at Estoril last time out.
Sunday is the last 990cc bike race before changing to 800cc next season.
Rossi, who claimed his fifth pole position of the season, had not been ahead in the standings until the race in Portugal last time out.
He will clinch the title if he finishes ahead of Hayden on Sunday, but Hayden can claim the title if he wins and the Yamaha rider fails to finish second.
"Sunday is the most important race of the year," Rossi told Spanish television afterwards.
"I will be fully concentrated from the first to the last minute. The bike is going very well and I feel comfortable."
Final qualifying times for Valencia MotoGP:
1 V Rossi (It) Yamaha 1:31.002
2 T Bayliss (Aus) Ducati 1:31.210
3 L Capirossi (It) Ducati 1:31.307
4 S Nakano (Jpn) Kawasaki 1:31.341
5 N Hayden (US) Honda 1:31.378
6 D Pedrosa (Spn) Honda 1:31.385
7 C Stoner (Aus) Honda 1:31.470
8 C Vermeulen (Aus) Suzuki 1:31.606
9 J Hopkins (US) Suzuki 1:31.663
10 C Edwards (US) Yamaha 1:31.711
250cc qualifying results:
1 H Aoyama (Jpn) KTM 1:35.109
2 J Lorenzo (Sp) Aprilia 1:35.450
3 A de Angelis (SM) Aprilia 1:35.539
125cc qualifying results:
1 A Bautista (Sp) Aprilia 1:39.058
2 H Faubel (Sp) Aprilia 1:39.288
3 S Gadea (Sp) Aprilia 1:39.499