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:

Pos.	#	Rider	Bike	Time	Gap
1	4	Andrea Dovizioso	Ducati	1'55.366
2	46	Valentino Rossi	Yamaha	1'55.427	0.061
3	93	Marc Marquez	Honda	1'55.743	0.377
4	29	Andrea Iannone	Suzuki	1'55.816	0.450
5	99	Jorge Lorenzo	Ducati	1'55.888	0.522
6	5	Johann Zarco	Yamaha	1'55.943	0.577
7	35	Cal Crutchlow	Honda	1'55.989	0.623
8	42	Alex Rins	Suzuki	1'55.997	0.631
9	9	Danilo Petrucci	Ducati	1'56.076	0.710
10	53	Tito Rabat	Ducati	1'56.111	0.745
11	25	Maverick Viñales	Yamaha	1'56.130	0.764
12	26	Dani Pedrosa	Honda	1'56.265	0.899
13	41	Aleix Espargaro	Aprilia	1'56.313	0.947
14	19	Alvaro Bautista	Ducati	1'56.528	1.162
15	55	Hafizh Syahrin	Yamaha	1'56.544	1.178
16	43	Jack Miller	Ducati	1'56.680	1.314
17	44	Pol Espargaro	KTM	1'56.999	1.633
18	45	Scott Redding	Aprilia	1'57.115	1.749
19	30	Takaaki Nakagami	Honda	1'57.183	1.817
20	12	Thomas Luthi	Honda	1'57.211	1.845
21	21	Franco Morbidelli	Honda	1'57.273	1.907
22	38	Bradley Smith	KTM	1'57.389	2.023
23	10	Xavier Simeon	Ducati	1'59.151	3.785
24	17	Karel Abraham	Ducati	1'59.462	4.096