Yamaha's comeback MotoGP star Valentino Rossi helped soothe two poor seasons at Ducati with a competitive performance during day one of 2013 MotoGP testing at Sepang.

Just days shy of his 34th birthday and over two years since his last MotoGP win, at the same Malaysian circuit in 2010, the seven time champion was fast from the off on Tuesday.

Riding alongside all his 2013 opponents, The Doctor was 0.264s from the top at the end of the opening hour, then moved to the head of the standings at midday. Rossi was later pushed down to fourth, but a competitive 0.427s from pace setter Dani Pedrosa around the two-minute plus lap.

The Italian admitted his performance had been a 'big relief'.

"It was a big relief, because after two seasons like this you have a lot of question marks, a lot of doubt. Am I still a top rider? Am I still able to arrive at the limit with the bike?" said Rossi, speaking in the Sepang paddock after the close of testing.

"In the last two seasons the results were quite bad, but especially the difference to the top guys was huge. It was not half a second, it was 1.5-2 seconds. So for me it is a great relief today.

"What I understand in my career is that the feeling after ten laps is very important... and I was straight in the top three this morning.

"When I tried the Ducati at Valencia after three laps I understood it would be very hard. You never give up, but the first impression is very important."

Rossi also praised the M1's clear response to set-up changes and indicated that he has achieved two of the three goals he had set for the test.

However the most important target will have to wait until Thursday.

"My targets for this test were feeling with the bike, the way to work on the bike and - especially for me the most important thing - the distance to the top by the third day," he said.

"Today the difference is 0.4s and I am happy. We hope to improve day by day. If I am second, third or fourth [on the timesheet] it is not a big deal."

With rain blighting Rossi's comeback test for Yamaha at Valencia and Aragon last November, Tuesday marked Rossi's first real test on the 1000cc M1.

"The base set-up I started with was similar to Lorenzo, with some small modifications from past experience of the M1," Rossi explained.

"So as an example, I usually use one rank harder front spring than Jorge. But at the end the settings are very similar.

"This morning I used the 2012 bike from Valencia. This afternoon I tried the same spec, but with a different engine. The 2013 modification.

"I only made short runs because the first day of the first test is the hardest physically. If you try too much today you have a bad feeling for the rest of the test. So I tried to save same energy.

"But I did a 2m 2.0s [matching the official race lap record] with 27 laps on the rear tyre - seven laps more than a race - so for me race distance is not a concern."

Commenting on the challenge of taking on team-mate and reigning double champion Jorge Lorenzo, plus last year's title runner-up Pedrosa, the #46 said:

"For sure the level is so high and for me it is difficult because I have to try to beat Lorenzo and Pedrosa, who think are at the top of their career.

"I am older so I need to do more effort, but we are not so far."

Rossi added that the performance of rookie Marc Marquez - third fastest behind Pedrosa and Lorenzo, with a lap time just 0.044s from the top - underlined his belief that the Moto2 champion can fight for victory from the very first race.