Ducati's Andrea Dovizioso set the pace the opening practice session of the 2018 MotoGP season in Qatar, just 0.061s ahead of Valentino Rossi.
Carrying over his impressive form from the third and final pre-season test at the Losail circuit, Dovizioso grabbed the top spot with three minutes remaining of a first session held in daylight hours.
He set a best time of 1m55.366s to oust Rossi from the the top spot by four tenths, and while the factory Yamaha rider improved in the dying stages his 1m55.427s effort left him just over half a tenth shy.
A last-minute improvement for reigning champion Marc Marquez put the Honda rider third, 0.316s behind his 2017 title adversary Dovizioso, with Andrea Iannone making it four different manufacturers in the top four on board the best of the Suzukis.
Jorge Lorenzo led the way in the opening stages on the second works Ducati but ended up slumping to fifth, a little over half a second behind teammate Dovizioso.
Best of the privateers was Johann Zarco on his 2016-spec Tech 3 Yamaha, ahead of LCR Honda man Cal Crutchlow and Alex Rins aboard the second Suzuki.
A pair of Ducati satellite riders, Danilo Petrucci (Pramac) and Tito Rabat (Avintia) completed the top 10.
Maverick Vinales was 0.764s on the second of the factory Yamahas in 11th, one place ahead of Dani Pedrosa on the second Repsol Honda.
Aleix Espargaro was 13th fastest with his Aprilia, now equipped with the latest-spec engine that had been due to come on stream in Qatar testing before being delayed.
KTM's charge was led by Pol Espargaro in 17th, the Spaniard joining Thomas Luthi and Alvaro Bautista in crashing during the opening session.
Last-minute Tech 3 Yamaha replacement Hafizh Syahrin was top rookie in 15th place.
First practice results: