Victoria Pendleton exceeded all expectations by finishing fifth on Pacha Du Polder in the St James's Place Foxhunter Chase at Cheltenham.
Pendleton gave the Paul Nicholls-trained nine-year-old a very patient ride and was stone last for the first mile.
As the race began to evolve, Pendleton, a double Olympic cycling champion, began to move through the field with style.
Dependable in the jumping department, Pacha Du Polder was making lengths at some fences but turning into the straight Pendleton still had plenty of horses in front of her.
As Nina Carberry brought Enda Bolger's champion hunter On The Fringe (13/8 favourite) through to beat Marito by a neck, Pendleton stayed on strongly to complete an afternoon to remember.
Pendleton, whose mount earned £936 in prize-money for fifth, said: "I can't believe how nice the crowd has been, I'd like to thank Alan and Lawney Hill, Andy Stewart (owner) and Paul Nicholls, they've made this all possible.
"I feel honoured to have been given this opportunity. It's right up there with everything I've ever done, it's such a rush. Thank you to all the jockeys that have been involved today, they've all been so nice and I feel really lucky. I think it's one of the greatest achievements of my life, a special achievement."
Stewart is hoping the rules governing amateur licences will be changed in order to allow Pendleton another bite of the cherry over the Grand National fences in the Fox Hunters' Chase at Aintree.
He told BBC Radio 5 Live: "All the dissenters said she would fall off at the first, but I've had plenty of my jockeys fall off at the first. She got round nicely and the horse looked after her.
"I just hope the rules will be changed between the Category A and B licences so she can ride him at Aintree. As far as we are concerned, he will go to Aintree for the race he finished second in last year. She's got to have a couple more rides under Rules or the rules have got to be changed to ride at Aintree. What Victoria has done today is magnificent, she is a credit to the sport."
Nicholls said of the ride: "That was the only the way to ride him - hunt, hunt, hunt. She went for a clear round, took her time and in the end was not beaten far.
"She was brilliant. I never doubted she would be OK. It was an absolutely super ride."
Grand National-winning trainer Oliver Sherwood said: "I thought it was a 12 out of 10, let the knockers knock, it was a great ride.
"It was just a shame she was not in the top four. She had never ridden a year ago and I take my hat off to her. I think we should embrace it, as it is very good for racing."
Carberry said of her winning ride: "I'm so happy, I didn't think I had a chance turning in but he winged the last and he's always there for you.
"I was expecting a better gallop so I could use his jumping a bit more.
"I missed the third-last and lost a few lengths and thought my chance had gone, but I winged the last two.
"He loves the spring ground, it brings out the best in him, it's a dream come true.
"Enda is unreal at getting them to peak for the big day. Well done to them and I'm just delighted to get to ride him."
Bolger said: "It's exciting to go back-to-back in this but it's a race in which we had a little bit of everything. Clapping Victoria on the way back as well as Nina - it was a fantastic performance by both women.
"He hadn't run since Punchestown in April when he came back to the track and as he done very well in his spell at JP's (McManus) place, he was burly and needed the race. We had him ready today to pull out all the stops and we are on cloud nine again.
"I thought Victoria's performance was second to none."
Victoria Pendleton fence by fence
START: With doubts about Pacha Du Polder's stamina over this extended three and a quarter miles, the double Olympic cycling champion had her mount away from the potential pacesetters and 23 rivals as the tape went up.
FENCE 1: Pacha Du Polder jumps the first tidily but in last place.
FENCE 8: Now settled into a nice rhythm and jumping well, Pacha Du Polder jumps past one rival, Camden.
FENCE 12: Pacha Du Polder passes a few more rivals but is still well towards the back of the field with one circuit left.
FENCE 14: Pacha Du Polder is still fifth-last at the water-jump but the race has really yet to begin.
FENCE 15: Jumping an open ditch, Pendleton is getting a fine tune out of Pacha Du Polder, who is serving her well by jumping superbly.
FENCE 19: Pacha Du Polder has crept his way into 10th and looks to have more running left in him.
FENCE 22: Once over the final fence, Pendleton gets stuck in and rides a tremendous finish as Pacha Du Polder weaves his way through to take fifth place, just behind the placed horses.
CONCLUSION: An amazing effort by Victoria Pendleton, who fully justified the decision for her to take part in the amateur riders' Gold Cup. After making all when winning at Wincanton, she showed she could deliver contrasting tactics in a bid to conserve Pacha Du Polder's energy. To mix it with some talented jockeys, including Nina Carberry, Jamie Codd and Sam Waley-Cohen, was remarkable for one so inexperienced and with the cameras well and truly fixed on her. She brought her mount into the winner's enclosure to receive the generous applause of an appreciative crowd.
