Harbour Law took a dramatic St Leger as favourite Idaho unseated his rider

Laura Mongan became the first woman to train a St Leger winner as Harbour Law triumphed at Doncaster, as favourite Idaho stumbled and unseated his rider.

The complexion of the race changed dramatically three furlongs out when Idaho, who was in mid-division and seemingly going well under Seamie Heffernan, took a bad step, stumbled and lost his rider. The stewards held an inquiry into the incident but were unable to apportion any blame to any other horse.

Idaho's exit from the race left stablemate Housesofparliament to throw down a challenge to leader Ventura Storm, who had seen off Sword Fighter, but all the while George Baker was bringing the winner closer to the lead in order to throw down his late challenge.

The 22/1 chance's proven stamina kicked in as he stayed on relentlessly to cut down Ventura Storm (14/1) and Housesofparliament (7/1) in a thrilling finish.

Mongan, assisted by her husband Ian, a former jockey who retired in 2013 having spent his final years as a rider working for Sir Henry Cecil in Newmarket, was also sending out the first Classic winner trained in Epsom since Right Tack's success in the 1969 2000 Guineas.

"We saw him in the paddock and we couldn't believe how well he looked," she said. "It's all a bit surreal at the moment - a lot of screaming - but this is brilliant.

"George has ridden the horse all the time. He knows exactly what to do and we left it all in his hands today as we knew he would know what to do."

Speaking to Channel 4, Ian Mongan added: "We've had a lot of faith in this horse but did we think he would win the St Leger? Maybe. He has come up against the best of the best. From a little yard in Epsom, we are taking on the mighty power of Coolmore and all the other trainers.

"Henry Cecil sat me down three or four years ago and told me that good horses make good trainers and jockeys and that is exactly what happened today. He is a good horse. We were lucky that he came into our yard and all you have to do is feed them well and train them well and they've got engines and take you to special places. This horse has taken us to the St Leger - a Classic race. No woman trainer has ever won this race and Laura has done it today.

"Laura's a fantastic trainer, a fantastic wife and a fantastic mother. We left our seven-month-old daughter Daisy at home today to come here on her birthday and now we've justified it.

"To train a St Leger winner, I can't quite believe it. I rode in the Derby and the 2000 Guineas but never in the St Leger. This means so much to me and to Laura and the family and the yard. Epsom has struggled since the rise of Newmarket and Lambourn. Hopefully, this will put it back on the map.

"I can't get my head around the fact that this horse has won the St Leger. We came into today hoping he would run well and we thought we could only dream that he'd win but he has. He's such a lovely horse.

"Of all the horses we have who are rated 50, 60, 70, 80, he is the easiest horse to train. This good horse has come to our yard and he has put us on the map. He's very professional and he's a class act.

"I hear a noise at 2am. I go out in my boxer shorts into the yard to see how he is. That's not so much the stress, but what this means. This horse and this win means everything and I am going to celebrate it. I pray he isn't sold and that he'll be a lovely Cup horse for us next year."

Nick Cornwell, who owns the horse with wife Jackie, said: "We were praying for rain on the way up and when we got about 15 miles on the track it stopped and we thought that might be that but he was the best horse on the day.

"We'll sit down now and make a plan. He's progressed as the year has gone on and I think he will progress again next year.

"Between myself and Jackie, we've been involved in racing for more than 20 years, we have a pre-training yard in Whitcombe, but we've never experienced anything like this."

Baker described victory as "a sweet, sweet result".

"I am so happy for Laura and Ian (Mongan - former jockey and Laura's husband) because they have had so much belief in him," he said.

"They have done everything right - they have given him plenty of time between his races and it has 110 per cent paid dividends for them. 

"It's an amazing feeling. It was a hard day yesterday and I find that you have to get over it, work out if you think you can make any improvement and get on with it.

"I worked him at Kempton about two weeks ago and he felt brilliant. I kind of felt that we all had Idaho to beat and, when they had that incident, it made it a very open race."

After receiving medical attention, Heffernan was able to walk away from his fall and Idaho galloped past the winning post riderless just behind the placed horses.

"That wasn't part of the plan!" said Coolmore spokesman Kevin Buckley. "Fair play to Laura Mongan. It's a great result for her. Is it the Classic that got away? Very possibly. We'll sleep on it."

Ventura Storm, owned by a 12-strong syndicate of the Middleham Park Racing, is trained by Richard Hannon who said: "He has run a great race and he looked like he was going to win for most of the straight but got chinned.

"I am a little disappointed not to win but I could not be more pleased with the horse - he has run a super race and the owners are delighted.

"I bought George Baker breakfast this morning and then he does that to me!"

Heffernan was detained for treatment by the racecourse doctor and missed the ride on Found in the Irish Champion Stakes. He was believed to have suffered a facial injury.

Buckley commented: "He seems fine, but because he's had a bang on the head the doctors wanted to send him to Sheffield Hospital for a precautionary scan."

Speaking later from Leopardstown, Aidan O'Brien said of the Idaho incident: "It's racing - there is no law. There are so many variables and that was one that you couldn't think of happening.

"He put a foot on a divot and it just went away and it just unbalanced him. It's just amazing. What were the chances of that happening?

"Seamus is on the way to get scans, but he's grand. I spoke to him on the phone. He said he was cantering."

As for Housesofparliament, the Ballydoyle trainer said: "It was a little bit unfortunate when it happened as Colm (O'Donoghue) probably had to commit but he ran a good race.

"When that happens in a bunch a lot of stuff changes very quickly."

John Gosden trained the fourth-home Muntahaa and said: "What a race it was. Ventura Storm was in front there, with Silvestre de Sousa about to win his first Classic, Housesofparliament in front there, and then suddenly the winner comes from nowhere and does them both. Amazing drama with the hot favourite unseated in front of a big crowd of 30,000 and I am delighted for connections of Harbour Law.

"Let's hope Seamie Heffernan and Idaho are okay. They say that the horse must have stumbled, but it looked like he might have clipped heels to me."

Interestingly, Oisin Murphy reported after the race that he himself had been "lucky not to come down" aboard seventh-placed Ormito having hit "a false patch of ground".

Asked about the aggressive frontrunning tactics employed upon Muntahaa, Gosden replied: "Let's just say that wasn't the plan."

Jockey Paul Hanagan explained: "They didn't really go quick enough for me so I had to make my own running. He was also a bit to keen. He made the running at Chester and is maybe still thinking about that."