Jorge Lorenzo revealed that front tyre graining was the reason for his loss of speed, after leading the early stages of Sunday's Catalunya MotoGP.
The reigning world champion blasted past pole sitter Marc Marquez into Turn 1 and continued to head the field for the opening six laps.
But he then began to drop back through the pack, and was down in fifth place by lap 12 of 25.
“At the beginning I made a good start and with new tyres I was more or less at the same level as the other riders. But as I knew before the race, if I started to have graining on the front tyre I will struggle. This is what happened,” said Lorenzo, speaking to the trackside media.
“Rossi, with the same bike, didn't have so much graining. Looks like he rides differently than me and he can save more the front tyre, normally. Also he is very good in difficult conditions, in conditions with no grip.
“Today he made an unbelievable race. I could not ride like him and could not change my riding style to avoid the front tyre problems, in all the weekend. This is the truth.”
After fighting the tyre issues for 17 laps, Lorenzo was taken out of the race by Andrea Iannone
A second DNF of the season leaves the Spaniard 10-points behind new world championship leader Marc Marquez, who finished second to Valentino Rossi on Sunday.