Sepang MotoGP test: Rossi says Yamaha already doing better than '17

Rossi was the only rider to set a time below 2m01s for an hour of the session before being joined by team-mate Maverick Vinales, although the factory Yamaha riders finished their running early and eventually dropped to sixth and 13th respectively.

Throughout last season Rossi and Vinales struggled with Yamaha's 2017 chassis, rear tyre degradation and performance in mixed conditions, leading the team to revert to the 2016 bike as the base for this year.

"I don't remember one day like this last year," said Rossi.

"I was always competitive. I am happy because in November [at the private Sepang test] we did a good job, we understood [things] better after the confusion during the season.

"Today's chassis is a new chassis, an evolution but based on the 2016 [chassis].

"When I ride this chassis I feel better, my ride is more natural, I feel I perform better and when I push, I have good speed."

Rossi also revealed that he was using different engines in an effort to improve acceleration, as well as working on the electronics to fix the degradation problems.

He avoided longer runs to conserve energy, saying that the first day after the winter break at Sepang is a "disaster physically", and he is still recovering from the broken leg he suffered last season.

Vinales felt that big gains had been made with tyre management, although he still expects the Yamaha to develop further.

"There is a real improvement because from lap zero to lap 20 I just really do [lap within] 0.3-0.4s," he said. "That is very positive.

"I felt great with that, but still, I think we can improve a lot."