Jack Miller's MotoGP campaign has slumped from bad to worse after the Australian crashed out of the Portuguese GP.
Yamaha's Fabio Quartararo claimed a second consecutive victory after leading almost from start to finish on Sunday while six-times world champion Marc Marquez finished seventh in his first race in nine months.
Quartararo, who also won in Doha two weeks ago, opened up a 15-point lead at the top of the championship standings after three rounds.
Miller, in his first race since undergoing surgery to cure arm pump, was in the thick of the action in the top six when he slid off the track on the sixth lap.
After finishing a disappointing ninth in both of the season's first two races in Qatar, Miller, who had begun the season on his new factory Ducati with high hopes of challenging for the world title, is now having to play catch up.
Starting on pole position, Frenchman Quartararo made a sluggish start to slip to fourth place on the opening lap but he recovered to take the lead with 17 laps remaining and never looked back.
"It will be a great celebration for my birthday in two days," said Quartararo, who turns 22 on Tuesday.
"We did an amazing job. I was riding well, riding easy and still maintaining the gap at the front. Now we know what we need to work on to go fast."
Miller's teammate Francesco Bagnaia, who was denied pole position due to a yellow flag infringement in qualifying, rode a clinical race to finish second and Suzuki's reigning world champion Joan Mir rounded out the podium.