Starting from the back row of the grid, the legendary Italian produced a daring ride of typically swashbuckling style.
As the lights turned green he scythed through the field, ticking off back-marker after back-marker as if nothing could stop him. A capacity crowd gasped and shrieked as lap after lap he drew closer to the front.
Rossi's Movistar Yamaha team mate Lorenzo, meanwhile, also began the race looking every bit the champion-in-waiting. The Malaga born rider had taken a typically formidable pole position, and quickly settled into the pacey, efficient style that has seen him win so many victories throughout his career.
Lorenzo loves to lead from the front, and at first it seemed certain that Rossi would need to take second place to preserve his title lead.
But behind Lorenzo, the two Repsol Hondas of Marc Marquez and Dani Pedrosa refused to let a gap open up. As Rossi carved his way through all-comers, his team mate knew that his fellow Spaniards were on his tail.
Rossi went from 26th on the grid to 15th on lap one. By lap three he was ninth. With 14 laps remaining The Doctor took fourth place. But with an almost 12 second gap to the resurgent Dani Pedrosa it was clear that Rossi would need help from both Hondas to give him a chance.
For a while, that help appeared to be on its way. Lap after lap, Marquez held on to Lorenzo's rear wheel, without ever getting quite close enough to mount a passing attempt.
Pedrosa closed on the pair too, and with three laps to go the three Spaniards were almost together.
Then, just as Marquez appeared ready to move in for the kill, Pedrosa swept by his young teammate; but, the diminutive 30-year-old overshot the corner, allowing Marquez to strike back. The two were briefly elbow-to-elbow and off line, leaving Lorenzo clear to re-open a gap. It proved decisive.
Lorenzo thumped his fuel tank in delight as he crossed the line. Rossi, in fourth, could only wave sadly to his legion of fans in the 110,000 crowd. It had been an electric performance, in an astonishing race; a fitting grand finale to this most dramatic of seasons.
The newly crowned champion said he became aware of the two Hondas in the closing stages. "I knew I had two riders behind me and that, if they overtook me, I would lose the championship, so it was a very difficult situation," he said after the flag.
"On the last lap I passed the last corner and saw the checkered flag and I couldn't believe that I won the race and the championship in the last moment. It's such a relaxing and enjoyable moment. I was crying on the honour lap, it's such a fantastic day for us."
But the Spaniard later hinted that perhaps there had been a Spanish pact. Speaking to the Movistar Yamaha MotoGP channel he said, "They knew what I had in play. The fact they are Spaniards like me helped me," he said.
"That helped me because for sure in another kind of race they would have tried to overtake, which they didn't this time."
He also said Rossi would have enjoyed similar benefits from Italian riders. "If Valentino had been in my position and with Italians behind they would have done exactly the same. The title had to be for Spain."
Rossi, meanwhile, was quick to reignite his three week feud with outgoing champion Marquez. "I think that the situation was already bad, but today was embarrassing for everybody because it was unbelievable, the behavior of Marquez is something very bad for everything, especially for the sport," he told reporters.
Rossi went as far as to suggest Marquez had protected Lorenzo from Pedrosa. "It is something that nobody expects, because a Honda rider that made a Yamaha rider win and give the maximum just to push out his teammate is something that nobody expect and I think it is very, very bad news."
The Italian claimed the race had vindicated his previous statements about Marquez. "I am happy because now everybody see what I said in Australia and I don't understand the behavior of Marquez but sincerely for me it is very difficult to say something to him because I hope that he will understand what he did in these last three races in the future of his career."
He also hinted that the title win would be a hollow one for Lorenzo. "At the end I think that also Lorenzo have to not be very happy, as it is not a championship that was won on track. But anyway is memories."
Marquez, meanwhile, insisted he had given his all. "There were a few laps in which I was really on the limit, forcing the front tire - which moved around a lot," he said.
"With about six laps to go, I felt that we could win because I had caught up to Jorge. I did not expect Dani to come through so quickly, and when he passed me he ran wide. I used that to pass him back but Jorge had escaped by half a second making it impossible to recover the gap, even though I rode the last lap and the entire race at 100%."
Honda Racing Corporation's president, Shuhei Nakamoto, reacted angrily to Rossi's post-race words. "This is not the atmosphere we wanted to experience at the end of an unforgettable championship," he said in a statement.
"We understand that it's been a very difficult day for Valentino, after leading the championship for 17 races and losing by just five points in the final race must be very disappointing. However, on the other side we cannot accept the strong accusations he has directed against our rider and Honda in the past weeks and in today's post race press conference."
Nakamoto called on Rossi to cease his attacks. "We cannot accept that these accusations continue to surface time after time, as this is the perception of one person - which we respect - but it is not the reality."
"Valentino is a great champion and clearly an intelligent individual so we truly hope that in time, once the dust settles, he can re-evaluate what has happened and accept this was another great race from a wonderful season, and it's a shame to spoil it."
An emotional Lorenzo, who underlined his commitment to Yamaha before the race, refused to be comment on plans for next season. "I don't want to think about 2016 now. We will see later during the test, or after the test," he said.
"Now I just want to enjoy it with the team like crazy, to feel this moment completely with no end, because it's not easy to repeat and it's not easy to become champion again."
As 2015 season's acrimonious final chapter comes to a close, the almost unprecedented bad blood appears certain to trickle into next year's contest. With a change in tire manufacturer, shared electronics, and new riders, next season could be one to savor.