The rain in the morning had Rossi venture out on track, keen on working on the wet setting of his bike and confirming the findings the team made in the Valencia and Sepang tests they held back in November. Heading out with a new 2018 pre-season helmet, he ended the morning stint in 12th place.
As his afternoon session got under way, a dry track was waiting for the Italian, who took this opportunity with both hands. With three hours remaining, he put his 2018 bike to the test and set a provisional fastest time of 2'00.799s. As his teammate and various competitors started to pick up their pace towards the end of the session, the pack got reshuffled. Rossi responded by reclaiming first place on lap 44/50, and retired to the pit early. A flurry of activity in the last 15 minutes saw him end up in sixth position with a 2'00.233s, 0.806s from first.
Viñales was also eager to get going aboard his YZR-M1 this morning, to do a race simulation and start working on the electronics and engine specifications together with his teammate. The Spaniard came prepared with a special Sepang Test helmet too, with a design inspired by the famous artist Salvador Dali, and held fourth place at the end of his morning runs.
The 23-year-old looked comfortable out on track in the afternoon and he continued to put in lap after lap. As the pace of the field started to pick up in the drier conditions, he temporarily took over top billing from Rossi, clocking an impressive 2'00.758s. The competition got more and more heated towards the end of the day, but Viñales stuck to his testing schedule. He dropped a 2'00.714s on lap 55/72, which ultimately earned him 13th place, 1.287s from the front.