Yamaha MotoGP rider Maverick Vinales beat team-mate Valentino Rossi to lead the second day of 2018 pre-season testing at Sepang.
Vinales, who had finished only 13th on the first day as he focused on race runs, logged a 1m59.355s in the dying minutes of Monday's running, surpassing Rossi by 0.035 seconds.
Wet weather was again a factor, with the timing screens left empty for over an hour initially as the field waited for the track to dry out following overnight rain.
Once the action kicked off in earnest, Jack Miller, Pol Espargaro and Andrea Dovizioso were among those taking turns in the lead, before Rossi logged the day's sub-two minute laptime, a 1m59.766s.
Honda's reigning champion Marc Marquez soon joined Rossi below the two-minute mark, before Dovizioso overhauled his compatriot with a 1m59.732s as the session was approaching halfway.
The Ducati rider's benchmark stood for several hours, before it was narrowly beaten - first by Marquez and then by Tech3 Yamaha's Johann Zarco - as track action picked up towards the end of the day.
With just over half an hour left to run, LCR Honda rider Cal Crutchlow found a quarter of a second to go top, logging a 1m59.443s.
Rossi soon improved that to a 1m59.390s, finally bettering Dani Pedrosa's benchmark from the opening day, before Vinales edged ahead with 11 minutes left on the clock to end the session on top.
Crutchlow ended up third, with Ducati works rider Jorge Lorenzo and Pramac Ducati privateer Miller completing a top five split by just 0.154s.
Marquez slotted in seventh - behind Zarco and 0.002s ahead of Dovizioso - and ended his session with a late crash.
Pramac Ducati's Danilo Petrucci and Suzuki's Andrea Iannone made up the top 10, the latter's GSX-RR having caught fire early in the session.
Sunday pacesetter Pedrosa was only 12th, on a day Honda's all-new winged fairing made its official test session debut.
Aleix Espargaro led the way for Aprilia in 11th, while his brother Pol was the top KTM in 14th, despite ending his day after just 23 laps with a crash at Turn 4 that necessitated a 10-minute red flag.
Marc VDS Honda's Franco Morbidelli fell twice, but still ended the day as the top rookie in 17th.