There have been afternoons at the Cheltenham festival in recent years when it seemed that Willie Mullins had found a way to banish the ­abiding air of uncertainty that had always been the meeting’s motif in earlier times. Within the first 90 seconds of the Queen Mother Champion Chase on Wednesday, however, the script had been read and then rejected as far too predictable, as El Fabiolo, the 2-9 favourite, was pulled up with well over a mile still to run, leaving in tatters countless bets on a Mullins treble in the day’s Grade One events.

Captain Guinness and Rachael Blackmore, who finished nearly 15 lengths behind El Fabiolo last month at ­Leopardstown, were the pairing to take advantage, finishing one‑and‑a‑half lengths in front of Gentleman De Mee, a stable com­panion of the odds-on favourite.

Related: Cheltenham’s Style Wednesday rebrand annoys all the right people | Barry Glendenning

But the story of the race was as much about the horse that failed to win, as until the moment when El Fabiolo lost his hind legs at the fifth fence Mullins’s afternoon was unfolding entirely according to plan.

The trainer saddled the first five home in the opening Gallagher ­Novice Hurdle, and many of the punters who had put El Fabiolo in a treble with Ballyburn, the easy winner, and Fact To File, who took the Grade One novice chase 45 minutes later, were probably starting to count their winnings as El Fabiolo’s odds contracted steadily before the race. Cheltenham, meanwhile, was preparing to acclaim the 100th festival winner for the man who has come to dominate the meeting.

Those celebrations were not long delayed, as Mullins reached his ­latest landmark less than two hours later when Jasmin De Vaux – with ­Mullins’s son, Patrick, in the saddle – took the Champion Bumper at the end of the card. For many punters, though, the abiding memory of the day was of a failure that joins Annie Power’s last‑flight fall in 2015 as a moment when fortunes at the festival swung decisively in the bookies’ favour.

El Fabiolo was not foot-perfect at either the second or third before his race-ending mistake at the fifth. “He got very low over a few of them [in the early stages],” Mullins said. “I know he was a little bit chancy before, but I was very concerned. Then he jumped the last one [the fourth] good, but of course then he went on to the next one and just stood back too far at it and didn’t get high enough.”

The stands watched in stunned silence for much of the remainder of the race, until Blackmore and Captain Guinness moved smoothly alongside Edwardstone, the leader, with two fences to jump. After Edwardstone’s fall two out, Blackmore needed to keep the winner up to his work but had enough horse left to secure the unexpected success.

El Fabiolo returned sound and could attempt to restore his reputation at the Grand National ­meeting next month – and his owners, Simon Munir and Isaac Souede, gained a fair measure of compensation at the end of the card when Jasmin De Vaux came with a strong late run to give Mullins his 100th festival success.

“I can’t put into words what it feels like,” Mullins said, “because nobody ever thought that anybody would train 100 winners here. As I’ve often said, when I started out and had my first win here with Tourist Attraction, I thought that was a lifetime ­achievement, so I’m absolutely stunned that we’ve come this far.

“We have such a wonderful team at home. Having that team behind me is incredible, and for Patrick to ride it as well, and for one of our biggest owners.

“The team of owners we have, they all praise each other when they have a winner and console one another when there’s disappointment. They are the mainstay of the whole thing. Without owners none of us would be here. It’s their sport.

“We are just stunned that we have come this far, but we’ve had ­tremendous people behind us, ­backing us, the whole time.”

Patrick Mullins said afterwards that it was “a privilege” and “a ­special moment” to ride the landmark ­winner. Asked what it is that sets Mullins apart, his son said: “I always bring it back to the Gigginstown split in 2016, when we lost [Michael O’Leary] the biggest owner in racing and a third or a quarter of our horses.

“Instead of consolidating and maybe finishing second or third [in the championship], he went out and got more owners, more horses, more staff, more problems, and got bigger because of it. If that hadn’t happened, we might not be where we are now.

“He thinks outside the box and at times it can be like the man from the moon, but enough of it works.”