Zarco was the top Yamaha rider, moving up to second late on and, in an uncharacteristic day of action for the Frenchman, riding until very late on as he did more than 70 laps.
Monster Yamaha Tech 3 team-mate Hafizh Syahrin did only a handful less and was top rookie, completing the top ten
Nevertheless, the two together put in almost 100 laps for the Borgo Panigale marque and were only 0.092 apart by the end of the day.
Danilo Petrucci (Alma Pramac Racing) was P8 after just over 30 laps, but team-mate Jack Miller only did 13 - a crash after an issue on his first bike put paid to his plans,
Plenty to work on
Red Bull KTM Factory Racing's Bradley Smith, meanwhile, was P13 on the time sheets and did nearly 70 laps.
The sole KTM on track as test rider Mika Kallio remains sidelined following a German GP crash and Pol Espargaro recovers from a fall in the Czech GP, the Brit had plenty to work on as the constant development continues despite their tougher run of late.
Alex Rins (Team Suzuki Ecstar) was top Hamamatsu factory machine in P9 after more than 60 laps, and he was focused on electronics, the carbon chassis and a 2019 chassis.
Team-mate Andrea Iannone, however, had a shorter day - crashing early and sitting out the remainder of the day.
Test rider Sylvain Guintoli did get some good mileage despite his broken ribs, though, putting in 37 for the Japanese manufacturer.