Yamaha's revised factory-spec M1, widely savaged by its riders by the end of last year, made a perfect start to 2021 with victories for Maverick Vinales and Fabio Quartararo in the Qatar season-openers.

The bike has gone on to win four of the six races so far and leads the world championship by 24-points, but all of the post-Qatar victories – and title lead – has been courtesy of Quartararo.

No other factory-spec Yamaha has finished on the podium since Qatar, the other M1 rostrum being a third for Franco Morbidelli on the A-spec bike in Jerez, after Quartararo faded from the lead with arm pump.

The closest Yamaha to Quartararo in the world championship is now Monster Yamaha team-mate Vinales, in sixth and already 41 points behind.

Dividing success between rider and bike is always a thorning subject, but Morbidelli's Petronas team-mate Valentino Rossi credits Quartararo with delivering stand-out performances in most of the rounds so far.

"I think Quartararo made the difference," Rossi said after the Frenchman's latest victory at Mugello, which came despite the M1s being at bottom of the speed charts.

"But it’s not the first time this season because he made the difference in the second race in Qatar and also in Portugal he was very strong. In Jerez, he also made the difference but had a problem with his arm, then in Le Mans it was difficult conditions for the Yamaha, with half-and-half.

"At Mugello, Quartararo also rode at the maximum and never made a mistake and is very strong on the hot [qualifying] lap, which is very important now.

"I think he’s the rider in the better shape. He had some problem before with the arm, but if he's fixed this problem, he’s the favourite for the championship now because he’s the faster guy on track.

"The only guy this weekend at his level was Pecco. Unfortunately, Pecco did a mistake but if not, I think it could have been a very interesting the fight between Pecco and Quartararo."

The top two Yamahas in 2021 races so far:

Qatar 1: Vinales (1st), Quartararo (3rd, +3.0s)

Qatar 2: Quartararo (1st), Vinales (5th, +2.1s)

Portimao: Quartararo (1st), Morbidelli (4th, +5.1s)*

Jerez: Morbidelli (3rd, +2.5s), Vinales (7th, +5.7s)**

Le Mans: Quartararo (3rd, +14.5s), Vinales (10th, +40.6s)

Mugello: Quartararo (1st), Vinales (8th, +17.2s)

*Next best Factory-Spec Vinales in 11th, +23.8s.

**Quartararo fades from lead with arm pump.

Rossi himself finished the Mugello race as the third best Yamaha, two places behind Vinales, in a season-best tenth place.

Heading straight to Montmelo, Rossi returns to a track where last September he was holding second behind eventual race winner Quartararo, only to fall while trying to catch the young Frenchman.

In terms of speed, it was the last time that Rossi was competitive at the front of a MotoGP race and there are now only three events remaining until the summer break, when Rossi says he will take a results-based decision on his racing future.

"My pace during the Mugello race was decent," Rossi said, who was just 20th at the end of lap 1. "I was able to recover and make some overtaking. In the end I finished in the top 10, which was nothing fantastic but considering our situation now is not so bad.

"We modified something on the bike. Mugello has a lot of bumps so we tried to make a bike that gave me more feedback and was more smooth. Also we worked well with the electronics and in the race I felt not too bad. When I had free track in front my pace was not very far from the guys that fight for fifth and sixth position. We hope we can be competitive in Barcelona."

Rossi’s past Catalunya stats also include four pole positions, 14 podiums and seven victories in the MotoGP/500cc era.

"The Barcelona track is one of my favourites and I always really enjoy riding there. It’s a great place and I have some very good memories from it," he said. "We hope to continue improving and see what we can do."

Team-mate Morbidelli saw his Mugello race ruined when he had to ride through the gravel to avoid Marc Marquez fallen bike. The #21 has good memories of Barcelona after pole position and a close fourth place last year.

"Barcelona is another historical track and I hope that it will be good for us," he said. "Last year we were fast there, I took the pole position and so we have a good indication for our set from the 2020 race weekend.

"I expect that we can be on the same level as last year. I don’t know if it will be enough to be on top, as it is quite a tricky track, but we will try to do the best job that we can there. I’m really looking forward to facing another race this weekend."

Morbidelli is ninth in the world championship on 33 points with Rossi down in 19th with 15 points.