Tom Marquand and Scandinavia returned to huge cheers from the Doncaster crowd after digging deep for a Betfred St Leger first. The pair pulled out more when challenged by Aidan O'Brien-trained stablemate Stay True and fastest finisher Rahiebb.
Fellow leading Ballydoyle hope Lambourn - the English and Irish Derby hero - had no more to offer in fourth after setting a good pace under Sean Levey.
Marquand was one of the riders stepping in for O'Brien's number one Ryan Moore, who is expected to miss the remainder of the season due to injury.
Five years ago the winning jockey took the race for O’Brien's son Joseph on his horse Galileo Chrome and he said he was honoured to get the call-up.
"To be aboard for Ballydoyle is something special," he told ITV Racing after the 1m 6f feature.
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"He was so tough there, the ground is hard work. They were all coming at me and he fended them all off. I grew up watching Ryan ride winners like this."
Punters could be heard praising Marquand on the broadcast, as presenter Oli Bell completed the post-race interview.
"Doncaster is fantastic. It's nice winning a Leger with a few people here, it was a bit quiet last time," Marquand added.
When he opened his account in the prestigious staying contest, it was staged in front of a smaller capacity with strict Covid-19 social distancing measures in place.

Marquand, who grew up in National Hunt country near Cheltenham, only secured the ride the day before when Galileo Chrome's original partner Shane Crosse tested positive for the infectious disease.
Before this year's renewal, showers softened the racing surface which was officially described as soft, new conditions for Scandinavia.
But he proved he could handle them by holding Rahiebb by a neck, with Stay True a length-and-a-quarter back in third.
Coolmore's Kevin Buckley said: "It's fantatsic, we couldn't be more happy. He is improving every time. As Tom said when he got off the ground was softer than ideal for him but he still kept trying the whole time. Between sire and dam - she is a half-sister to the 'Iron Horse' Giant's Causeway - so I'm sure that's where some of the quality has come from.
"It's most important for us, we stand Justify in America and this is his second English Classic winner this year."
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