The 20-year-old first rode a YZR-M1 during a secret test at Almeria during the MotoGP summer break, but Valencia marked his first time working with the factory Yamaha team - which will be restructured next season to allow Valentino Rossi to race with Bridgestone tyres, while Lorenzo uses Michelin tyres.

Rossi has returned home for further treatment on his right hand, which he broke during qualifying on Saturday, but Lorenzo completed 52 laps throughout the afternoon and finished a creditable tenth with a best lap of 1min 34.320secs, just under two seconds from Ducati's world champion Casey Stoner.

"I'm very proud to be here in this garage and it's been quite an emotional day for me!" confessed Jorge. "I'm very happy to have the chance to try my new bike and I enjoyed myself a lot today. My first aim has just been to get comfortable on the bike and to try to understand as much as I can about it. I went very gently because the difference in power from my 250 bike is very big! I am definitely a long way from the limit but I think I made a good start. We need a lot of time and a lot of kilometres in order to learn about the bike, but I am looking forward to improving at each test."

"This afternoon the aim was to get Jorge comfortable on the bike - this is the most important thing at this stage," confirmed Lorenzo's team manager Daniele Romagnoli. "We adapted the handlebars and ride height to suit him and changed around a few other things to get him into the right position. We also worked a bit on the engine braking system because for him this is one of the biggest changes between a two-stroke bike, which is what he is used to, and a four-stroke MotoGP bike. He put in a lot of laps and it's been an interesting and exciting day for everyone. We're looking forward to having another whole day tomorrow."

"Today has been a sort of 'team launch' because we had new staff members joining the team and, above all, our new rider Jorge Lorenzo," added Fiat Yamaha team director Masahiko Nakajima. "I think that today we did a good job and it felt like there was a good atmosphere in our garage. We only had three hours of testing but Jorge completed 56 laps; more than any other rider today. Each run was more or less ten laps and this means that he was able to keep a high level of concentration. His attitude towards the development of the bike was very good. Jorge learnt a lot today and I am sure he will learn even more tomorrow."

Two other 250GP riders have graduated to MotoGP with Lorenzo; Alex de Angelis will ride for Honda Gresini and was 13th fastest on Tuesday, while 2007 title runner-up Andrea Dovizioso was 14th for the newly-formed JiR Scot Team.