Rins was one of the big headlines of the day, able to put in a substantial 61 laps on board his 2019 GSX-RR and was fastest for some time until deposed by Marquez.
He remained second after his earlier fast lap, however, and was the lead Hamamatsu machine by quite a stretch. Rookie team-mate Joan Mir ended the day in P23, just behind veteran French test rider Sylvain Guintoli.
Rossi in the hunt
There were positive signs from Yamaha on the timesheets. Vinales ended the day in P3 after 63 laps with a best of 1:59.937, with team-mate Valentino Rossi in P6 after 56 laps.
The Iwata marque are focusing on final decisions for their 2019 engine, the electronics and some chassis elements - and say comparing their times to competitors' is a key point of interest after an intense winter of work.
Just behind him came the first of the Mission Winnow Ducati machines in the form of new arrival Danilo Petrucci.
The Italian was just 0.003 ahead of Rossi after 54 laps. 2017 and 2018 runner up Andrea Dovizioso, meanwhile, ended Day 1 of 2019 in P8 with a 2:00.197.
Completing the top ten was an impressive day's work for Pol Espargaro (Red Bull KTM Factory Racing), who put in a fitting 44 laps with a best of 2:00.313 despite a crash at the end.
The Spaniard took the honours of lead Austrian machine by sixth tenths, although the second KTM on the timesheets was an equally stunning performance.