Yamaha's Maverick Viñales ended a busy second day of MotoGP testing at Sepang top of the times, ahead of team-mate Valentino Rossi.
The field was greeted by another damp to start to proceedings, though the circuit dried quicker than it did on Sunday, allowing most to get on with their programmes for the day relatively early.
Ducati's Andrea Dovizioso was the initial pacesetter on his GP18 with a 2:00.007s, before Rossi dipped underneath the two-minute bracket with a 1:59.766s.
The Yamaha rider enjoyed a positive start to the test on Sunday, a new chassis based on the 2016 version, as well as new engines and electronics updates yielding positive results for the Italian.
Trialing a new aerodynamic fairing, a revised design of the one first debuted at the Valencia test in November, a late effort of 1:59.390s sent him back to the top of the timesheets.
With 10 minutes on the clock, Viñales – who also spent the day evaluating Yamaha's new aero package – edged ahead of Rossi by just 0.035s.
LCR Honda's Cal Crutchlow was fastest of all briefly later in the day, but had slipped to third by the chequered flag.
Jorge Lorenzo took his factory Ducati to fourth on the timesheets as he continued to explore the capabilities of the Desmosedici's new chassis, with Pramac's Jack Miller once again completing the top five on his GP17.
Tech3 Yamaha's Johann Zarco felt after Sunday's running he was not competitive enough yet on the 2017 M1, though rectified this with a 1:59.702s which put him fastest of all for a time, before eventually ending the day sixth quickest and just 0.347s from top spot.
Marc Márquez continued to work on the three engine specifications Honda has brought to Sepang in seventh, with Dovizioso, Pramac's Danilo Petrucci and Andrea Iannone – who was forced to park one of his bikes in the afternoon due to a fiery mechanical failure – completing the top 10. A small fall in the final 15 minutes ended Márquez's day early.
Aleix Espargaró found the updated RS-GP allowed him to push harder into the corners, the Spaniard only half a second off of the pace in 11th at the end of Monday's running.
Sunday pacesetter Dani Pedrosa, trying a new seat unit and fuel tank on top of the new engines, was just 0.074s further back in 12th, ahead of Álex Rins on the second factory Suzuki and KTM's Pol Espargaró.
The latter was taken to the medical centre for checks after a crash in the afternoon, which caused a brief halt to the session.
Marc VDS' Franco Morbidelli was fastest rookie on Monday in 17th, despite a crash, with LCR's Takaaki Nakagami a couple of tenths back in 21st. Fellow rookies Xavier Simeon (Avintia) and Tom Luthi (Marc VDS) were 26th and 27th respectively.
