Valentino Rossi was half-a-lap from his first MotoGP win of the season - but left Le Mans empty-handed after losing the lead, then falling within sight of the finish.

The Italian superstar spent much of the race in a close third, behind factory Yamaha team-mate Maverick Vinales and Tech 3 Yamaha star Johann Zarco.

Rossi finally made his move on home rookie Zarco - running the soft, rather than medium rear tyre - under braking for the first chicane with 6 laps to go. He then pounced on Vinales at the same corner to lead with three laps remaining.

That ignited their first head-to-head duel and the young Spaniard kept the pressure on, diving under Rossi when the Italian ran wide at the slow Garage Vert double right-hander on the final lap.

But Vinales hadn't escaped and The Doctor immediately zeroed back-in on the youngster, closing through the Chemin aux Boeufs chicane, then again under braking for Garage Bleu, the penultimate turn.

Rossi was almost certainly ready for a last corner lunge, but never got that far - sliding off at the first apex of the Garage Bleu 'S'.

"It's a great shame because for me and my team it was the best weekend of the season, when I was more competitive in practice, in the wet and especially in the race. It was for sure my best race of the season," Rossi said.

"In the race the pace was always very high and in the middle part of the race I was in a bit in trouble with the front. I had a bit too much movement. So I tried to ride well, relax, because with more temperature it was more difficult than yesterday.

"But after, in the last laps, something changed. The balance of the bike came better, I was able to ride better and the first time I make a 32.6s [lap 14 of 28] I say 'f**k! Beautiful!'

"From that moment I ride well and I tried to attack. I overtook Zarco and after had the potential to fight with Maverick.

"Unfortunately on the last lap I did a mistake in Turn 6; I arrived a bit too fast and I don't stop. Maverick overtook me, but I knew I had another chance because I was very close and I tried to remain there. Because in Sector 4 I was good.

"Sincerely what happened in the crash, we don't understand, because usually you have to keep attention to the front, but I lose the rear. But anyway I am of the idea that when you crash you make a mistake and it's like this."

Could you see anything on the data?

"In Turn 6 maybe I arrived one kilometre faster, but was enough, because I lose the bike in braking and ran wide. This was the big mistake, because the other one was a consequence of the first.

"Sincerely the second crash we check deeply all the data and [shrugs]. Also from me, I don't feel too much, but I lose the rear, so something happened for sure. I did some mistake and I crash.

"Today I could really smell [the victory] because it was the perfect race. For sure it would be difficult with Maverick, because we still had the last part of the race track. But I was very strong, so I think that I was quite close to the victory and in the crucial moment I did the mistake."

Paddock rumours suggested Rossi may have used a little more rear brake than before at the corner where he fell.

Either way, the accident marked Rossi's first DNF since last year's Japanese MotoGP and saw him drop from first to third in the 2017 world championship standings, 23 points from Vinales and six from Dani Pedrosa.

"It's great shame to go back home with zero points and first of all I'm very sorry for the probable victory, but also the championship because I lost points," Rossi said.

"But it remains a very good weekend where I was strong. Now we have to see in the next race track, but [this year] I never ride like I rode this weekend, so we hope to continue with this speed."

Pedrosa's team-mate and reigning champion Marc Marquez also fell on Sunday and has slipped to fourth in the standings. Marquez has suffered two non-finishes out of the five rounds, with one DNF each for Vinales, Pedrosa and now Rossi.

The next event is Rossi's home Italian round at Mugello.