Valentino Rossi was gifted victory in the Czech MotoGP after Casey Stoner crashed when he was comfortably ahead.
Rossi extended his championship lead over Stoner to 50 points with the win.
Reigning world champion Stoner was one second clear of Rossi when, under no particular pressure, he skidded into the gravel on lap six.
His Ducati was too badly damaged for him to continue and Rossi went on to win, ahead of Toni Elias in second and Loris Capirossi in third.
Afterwards, Stoner told BBC Sport he was not quite sure what had happened.
"You know as much as I do," he said. "The bike was moving round quite a bit but that one just caught me out. No excuses, no nothing - it just caught me out."
606: DEBATE
"It was a long shot for the season - we gave too many points away and we needed to win these races. We did the best we could, but it's on to the next one.
"We're going to keep fighting race by race. The championship is very difficult but five or six races ago we were way out of it, so we've just got to keep plugging away race by race."
Rossi said he thought Stoner might have been trying too hard to make up for the ground he lost in the title race, when Rossi triumphed in their epic duel at Laguna Seca.
"I am sorry for him that he crashed but sometimes you make mistakes, especially when you have to recover points in the championship," he said.
"I have a 50-point lead, but there are six races to the end. Now we have a great setting and understand the tyres better."
Czech MotoGP race result:
1 V Rossi (Ita) Yamaha 43'28.841
2 T Elias (Spn) Ducati 43'43.845
3 L Capirossi (Ita) Suzuki 43'50.530
4 S Nakano (Jpn) Honda 43'54.700
5 A West (Aus) Kawasaki 43'58.306
6 C Vermeulen (Aus) Suzuki 43'59.449
7 M Melandri (Ita) Ducati 44'05.294
8 A De Angelis (SM) Honda 44'05.591
9 A Dovizioso (It) Honda 44'07.663
10 J Lorenzo (Sp) Yamaha 44'08.414
MotoGP championship standings:
1 V Rossi 237 pts
2 C Stoner 187
3 D Pedrosa 172
4 J Lorenzo 120
5 A Dovizioso 110
6 C Edwards 102
7 C Vermeulen 99
8 N Hayden 84
9 S Nakano 83
10 L Capirossi 77
11 J Toseland 75
250cc race result:
1 A Debon (Spa) Aprilia 41mins 08.168secs
2 A Bautista (Spa) Aprilia 41:08.448
3 M Simoncelli (Ita) Gilera 41:08.493
250cc championship standings:
1 M Simoncelli (Ita) Gilera 180pts
2 M Kallio (Fin) KTM 164
3 A Debon (Spa) Aprilia 139
125c race result:
1 S Bradl (Ger) Aprilia 41mins 05.176secs
2 M Di Meglio (Fra) Derbi 41:06.057
3 J Olive (spa) Derbi 41:09.246
125cc championship standings:
1 M Di Meglio (Fra) Derbi 186pts
2 S Corsi (ita) Aprilia 142
3 S Bradl (Ger) Aprilia 126
~RS~q~RS~~RS~z~RS~00~RS~)