Jorge Lorenzo looked in with an excellent chance of scoring back-to-back MotoGP wins after taking pole position for his home Spanish Grand Prix at Jerez, but the Fiat Yamaha star's victory hopes were to wilt in the heat.
Lorenzo dropped to third on lap one, then lost a further position to team-mate and eventual race winner Valentino Rossi on lap two.
The Spaniard later explained that - for unknown reasons - the warmer Sunday weather transformed the behavior of his M1 for the worse, and his eventual fightback came too late to trouble Rossi or runner-up Dani Pedrosa.
Nevertheless, Lorenzo was homing in on third placed Casey Stoner when he lost the front of his M1 and crashed out with four laps to go.
Lorenzo, who came into round three leading the MotoGP World Championship by one point from Rossi, is now joint third with Pedrosa, 24 points from the top.
“I am very sad, because I was so fast all weekend and on pole position. Unfortunately today the temperature meant that our setting did not work in the same way and at the moment we don't understand why,” said a downbeat Lorenzo, who turns 22 on Monday.
“This is really more disappointing than the actual crash. Fourth position wouldn't have been so bad but when you're in front of your fans, at home with so much adrenalin on the bike of course you try to do the maximum.
“I could see that the podium was possible and maybe the right thing would have been to go more gently and not push so hard in that moment, but I always want to do my best. Then I made a mistake and I threw all my good work away.
“We have to try to forget this and wake up feeling positive tomorrow because Le Mans is near. I'm sorry to all the fans who came to see me, to my team, family and to everybody,” he added.
Team manager Daniele Romagnoli said they were still to establish the cause of Lorenzo's race day problems.
“After excellent practice and qualifying sessions we expected to be on the podium but with the warmer temperature Jorge lost grip on the rear,” said Romagnoli. “We need to make a deep analysis of why we had these unexpected problems and make sure they don't happen again.”
Lorenzo had been just 0.039sec slower than Rossi in morning warm-up, but his best race lap was only fourth quickest, 0.319sec behind the #46.