Aidan O’Brien landed a seventeenth Breeders’ Cup success when Unquestionable played the role of super sub in the Breeders’ Cup Juvenile Turf at Santa Anita this evening.

Following the news of River Tiber's late withdrawal from the Breeders' Cup Juvenile Turf, all eyes were on Unquestionable as the Al Shaqab-owned runner was sent off the 13/8 market leader to land Aidan O'Brien a sixth success in the Grade 1 juvenile prize.

It was something of another Ryan Moore masterclass as the rider positioned the son of Wootton Bassett towards the inside rail after a smart beginning from stall eight. Unquestionable scraped the paint and gained a dream run through the inside before peeling out and quickening up smartly to put his rivals to the sword with a furlong to travel. Stablemate Mountain Bear ran on well from towards the rear of the field to ensure it was a one-two for team Ballydoyle, but ultimately the winning margin was comfortable and the 13/8 favourite had plenty to spare.

Aidan O'Brien, who was experiencing something of a rollercoaster day following River Tiber's withdrawal, said: "That's the way it is, I'm delighted for the lads. I felt so sorry for the lads [when River Tiber was withdrawn]. It's very tough to win here, it's unbelievable. When a day starts badly it usually spirals out of control. It was a great ride from Ryan."

The late withdrawal of River Tiber meant Ryan Moore switched to ride Unquestionable, who was originally booked to be ridden by Frankie Dettori, and O'Brien's retained jockey was certainly complementary about the performance.

He said: "I had a bit of speed underneath me. I ended up on the fence. We had the two coming here and we thought a lot of them both. He's done that really nicely today. I'm sorry for Frankie missing the ride."

It was back-to-back successes in the Grade 1 event for trainer Aidan O'Brien following Victoria Road's victory in the contest last year.