The pair were meeting for the sixth time and the 10-furlong Group One produced a similar result to the Coral-Eclipse at Sandown in July, as the pair went head to head in the final furlong before Roaring Lion got the upper hand on the line. Deauville was third.
The success by a neck takes the score to four wins for John Gosden's three-year-old, with 2000 Guineas hero Saxon Warrior having come out on top twice.
Whether we will see a seventh clash between the two remains to be seen, but owner Sheikh Fahad did not shy away from the big autumn targets and even hinted there may be another campaign to follow.
"The race panned out for Saxon Warrior than us," he said. "But his courage and turn of foot to go and get him was quite breathtaking to watch.
"The other Qipco Champion Stakes, the Ascot Qipco Champion Stakes, is definitely on the plans, the Breeders’ Cup is on the plans and I will have to discuss with John in the next couple of days and see how he comes out of this.
"Plans haven’t been finalized yet - he might stay in training, he might not. That will come later on."
Roaring Lion is now no better than Betfair's 9-4 for Ascot's seasonal finale on October 20, while the Breeders' Cup at Churchill Downs on the first weekend of November should now hold no fears for the once headstrong son of Breeders' Cup Turf runner-up Kitten's Joy. The race was a Win And You're In contest for the Breeders' Cup Turf, a 12-furlong race on a flat track that Gosden has mentioned before, although the Mile may also suit despite the lack of an automatic berth. Roaring Lion is 4-1 for the Turf with William Hill.
Should Roaring Lion appear on Champions Day, Saxon Warrior will not be meeting him once more.
O'Brien was satisfied with Saxon Warrior's effort and confirmed the Queen Elizabeth II Stakes remains the plan for the 2000 Guineas winner.
"He ran very well," O'Brien said. "The plan was always to go back to a mile at Ascot after this and that's where he'll go everything being well."
Roaring Lion was sent off the 8-11 favourite for the absent Gosden and Oisin Murphy, and the rider was content to sit at the back of the field with only French raider Study Of Man behind him through the larger part of the race.
In contrast, Ryan Moore took up a forward position on Saxon Warrior, as fellow Aidan O’Brien inmate Deauville set the pace, and it was Saxon Warrior who set sail for home with over a furlong to run.
Murphy never panicked. He stoked up Roaring Lion after finding himself wide on the bend and he produced another electric turn of foot to pull level with Saxon Warrior a handful of strides before the finish. It was enough. It was cool.
Earlier in the day Murphy had won for the first time in his native Ireland aboard Limini, who now looks bound for the Cesarewitch, and this was a seventh Group One triumph of the season for the 23-year-old. There could be more to come this season.
"Going a slow pace for Roaring Lion as he has a great kick," Murphy said.
"The complexion of the race changed a few times as we went along. We knew it was going to be tactical, but it was more tactical than anybody could have expected."
Asked whether he ever felt Roaring Lion might not prevail, as had occured at Doncaster in the Racing Post Trophy last season, Sheikh Fahad added: "I had a lot of belief in the horse. And John Gosden. And Oisin, who knows the horse well.
"It is a bit tricky when you come to a different country.
"That was his first time on a plane since he was a baby from Keeneland to England. To take all of that in his stride, and to do that on a race track was special. It was good for the fans and everyone."