Former MotoGP world champion Casey Stoner said he was "surprised" by how comfortable he felt back on a Ducati for the first time since 2010.
Ducati signed Stoner at the end of last year to return as a test rider for the Italian manufacturer in 2016.
The 30-year-old won his first world championship with Ducati in 2007 before moving to Honda in 2011 and sealing a second world title.
Stoner retired from the sport in 2012, but has since spent stints in touring car racing as well as a test rider for Honda.
The Australian completed 54 laps of the Sepang circuit in Malaysia on Saturday and admitted he was surprised with how he handled his return.
"It was a very positive day," Stoner told media after the test. "I was surprised by how it went, I didn't expect to be comfortable on the bike so fast.
"The front felt a little strange, but I was riding a new bike and on Michelins. There is room for improvement, but I think it's a good package, and every step we made is headed in the right direction.
"I found some good things and others we need to work on, like with any bike.
"The engine is fantastic, and [its other strengths are] the stability under braking and in slow corners. As for the rest, it's difficult to know if my feelings are because of the tyres or the chassis.
"The engineers are beginning to understand my language and I'm giving them my views, I think this is the most important thing. I was able to give them feedback despite it being only the first day.
"I'm a tester, not a racer, and I don't have specific goals. My job is to help."