Yamaha's Valentino Rossi hailed his exhilarating win in Qatar on Sunday as "one of the best" in his career, while applauding Ducati's strong start to the 2015 season.

Rossi passed Ducati's Andrea Dovizioso on the second-last lap of the race at the Losail International Circuit and then held off his fellow Italian to claim the chequered flag in a stunning finish.

It was Rossi's 70th win in MotoGP's premier class and the 36-year-old rated it highly.

"This was one of the best victories for me," Rossi told MotoGP's website.

"The bike was fantastic, I never gave up but it was a real fight with the Ducatis and the Hondas who were really strong."

With Dovizioso and Ducati team-mate Andrea Iannone completing the podium in Qatar, Rossi argued the Italian team will challenge Japanese outfits Movistar Yamaha and Repsol Honda this year.

Rossi added he believes he can keep racing for four more years, while he was also pleased to see reigning champion Marc Marquez of Repsol Honda slump from the front row to last on the first corner in Qatar, before having to settle for fifth.

"I feel good, I have good motivation and I like my job because it is also my passion, like all the guys here. For me, if you live a good life, good training, you can ride at the top until 40-years-old," Rossi said, according to crash.net.

"What makes the difference is more the motivation and the concentration.

"So I am so happy because Marc is behind, which is very important for the championship, but this year I think there will be six instead of four [title challengers], because the two Ducatis are very strong and they are riding in a good way, so it will be very interesting."