* Vinales wins delayed race from pole position
* Spaniard a winner on Yamaha debut
* Rossi on the podium at 38 years old
* World champion Marquez finishes fourth (Adds detail and quotes)
March 26 (Reuters) - Maverick Vinales won a rain-delayed and shortened Qatar MotoGP season-opener on Sunday in a triumphant Yamaha debut for the young Spaniard.
Italian Andrea Dovizioso was second for Ducati with compatriot Valentino Rossi, at 38, back on the podium in third place for Yamaha under the floodlights.
Honda's reigning champion Marc Marquez finished fourth on an eventful evening that saw 22-year-old compatriot Vinales drop from pole to fifth on the opening lap before making a stirring comeback for his second career victory.
The season's only night race started 45 minutes late after earlier rain, with plenty of discussion among the riders who did two warm-up laps before Vinales took his position at the front of the grid.
The race was shortened to 20 laps, a day after qualifying was abandoned due to bad weather.
Italian Andrea Iannone took the lead at the start, with French rookie and twice Moto2 champion Johann Zarco powering through from the second row to slot in behind, with Marquez third.
Zarco, on a non-works Tech3 Yamaha, then went in front and began to pull away in what would have been a sensational outcome had he not crashed six laps later.
Iannone also fell, leaving Dovizioso fighting the Yamahas and Marquez before the latter faded.
Vinales and Dovizioso traded the lead before the Spaniard, a race winner last season for Suzuki, made his move stick on the penultimate lap.
"It feels great. The track was so difficult," said the winner.
"First lap I was taking a lot of care, then when the people started to push I said 'OK, now is the time to push' and I started to come back little by little -- I didn't want to destroy so much the tyre.
"Anyway, the bike was great," said the Yamaha rider, who had been fastest in every pre-season test before arriving in the Middle East.
Rossi, a nine times world champion, started 10th and raced with a camera dangling off the back of his bike after making contact with Britain's Cal Crutchlow into the first corner.
"If I had to bet on me, on my podium today, I don't bet for sure," said the happy Italian.
"But we never gave up. We tried the maximum, we tried three or four different settings this morning... but I enjoyed it a lot."
Spain's triple champion Jorge Lorenzo, last year's winner in Qatar whose place at Yamaha was taken by Vinales after he moved to Ducati, finished 11th. (Reporting by Alan Baldwin; Editing by Clare Fallon and Ken Ferris)