MotoGP championship leader Andrea Dovizioso headed Austin race winner Marc Marquez by just 0.007 seconds in a Jerez FP1 session that had the top 19 covered by just one second.
Dovizioso's Ducati team-mate Jorge Lorenzo, who took his maiden podium with the Italian marque at this race last year, was the early pacesetter on his GP18 with a 1:40.727s, the Spaniard testing a 2017 specification seat unit this morning.
Marquez deposed his compatriot just moments later with a 1:39.548s, which stood as the benchmark until the final seven minutes, though Honda stablemate Cal Crutchlow on the LCR bike matched him midway through the session.
A flurry of fast laps in the closing stages saw top spot change hands a number of times, with Yamaha's Valentino Rossi the first to beat Marquez's time with a 1:39.488s.
This was short lived as, benefiting from a tow from the Italian, KTM's Pol Espargaro – who agreed a new two-year deal to remain with the Austrian marque next year – took his RC16 to the top of the timesheets with a 1:39.311s.
Marquez returned to the top of the standings a minute after Espargaro with a 1:39.275s, though was denied top spot at the chequered flag by Dovizioso, who managed to go 0.007s quicker than the Honda rider, despite getting caught in traffic on his final lap.
Espargaro hung onto third spot, while Pramac's Danilo Petrucci slotted into fourth at the end ahead of team-mate Jack Miller and Rossi.
Johann Zarco – who will join Espargaro at KTM next year – guided his Tech3 Yamaha to seventh, with Crutchlow, Maverick Vinales and Aprilia's Scott Redding completing the top 10.
Austin podium finisher Andrea Iannone was just 0.029s outside of the top 10 in 11th, while KTM wildcard Mika Kallio – who is testing a prototype 2019 RC16 this weekend – followed him in 12th.
Aleix Espargaro was 13th on the second RS-GP, with Dani Pedrosa, who is still recovering from the wrist injury he suffered in Argentina, and early session leader Lorenzo rounding out the top 15 at the end of FP1.
