MotoGP world champion Casey Stoner shrugged off an ailing back to post the fastest time Wednesday in pre-season tests on the sport\'s new 1,000cc bikes at Malaysia\'s Sepang circuit. The Australian Honda rider, who won the championship in 2007 and again last year, had been sidelined on day one Tuesday after pulling a back muscle while stretching. But he bounced back to outpace his Yamaha rivals in conditions that, while hot and humid, were drier than on day one and led to faster lap times as teams appeared to get the feel for the new bikes. Stoner, who won 10 races last season, hit the top of the timesheet in late practice runs, logging 2 min 00.895 seconds while his Honda teammate Dani Pedrosa of Spain was fourth with a time of 2:01.508. \"When I went out the track was good. The bike was performing pretty well. It was nice to feel the wind on your face again,\" Stoner told reporters. MotoGP has moved to 1,000cc bikes this year in place of the earlier 800cc engines. American Yamaha rider Ben Spies, who was fastest in early practice Wednesday, ended up in second place on 2:01.052 while his teammate Jorge Lorenzo of Spain, the 2010 world champion, was third with a best time of 2:01.068. Yamaha\'s British rider Cal Crutchlow rounded out the top five with a time of 2:01.565. \"Yamaha (is) looking strong and competitive,\" Stoner said. \"Jorge is doing a great job. Ben is starting the season strong. Hopefully they can continue that.\" The testing session marked an emotional return for riders to the Sepang circuit for the first time since Honda rider Marco Simoncelli died there in a shocking crash in October\'s Malaysian MotoGP. Seven-time world champion Valentino Rossi of Ducati, who is looking to make up for a disappointing 2011 campaign, ended in 7th place on 2:01.886. The 32-year-old Italian last year failed to win a race for the first time in his 15-year career. Testing ends Thursday and is followed by another three-day session at Sepang beginning February 28. The MotoGP 2012 season will officially start April 8 in Qatar.