The chestnut defeated Somersby and Module comfortably by six lengths, a result which caused an eruption in the stands and led to a standing ovation from a host of jockeys next to the winner's enclosure.
Jamie Moore was the jockey who rode Sire De Grugy home with aplomb. He is a chip off the old block of his father, Gary - who is also Sire De Grugy's trainer - since both are popular figures in racing. They are similarly unaccustomed to the success earned yesterday, too.
Their horse was an inexpensive purchase and belongs to Steve Preston, a lower-profile owner than most rubbing shoulders in a Queen Mother. Preston had never owned a horse before and was only coerced into the exercise when his friends and family deposited money into a bank account for his 50th birthday.
His victory could be cheapened by acknowledging that last season's champion, Sprinter Sacre, has been sidelined, but Sire De Grugy could have done no more during the campaign to earn a victory at Cheltenham.
He was sent off as a surprisingly generous 11-4 favourite, but it proved a straightforward march to the line as Moore hung back from the fierce pace set by Special Tiara, Somersby and Arvika Ligeonniere and let fly at the second-last turn.
"It annoys me that people don't give [Sire De Grugy] the credit he deserves," said Moore Snr. "It was all about Sprinter Sacre and someone wrote the other day that this race should be done under the trade descriptions act because the Queen Mother Chase isn't right."
Gary Moore's father Charlie was also a trainer and worked from ramshackle premises in Brighton before moving to more upmarket Horsham. The family has been cast in a story of unanticipated success, although Moore was unsure why the win yesterday should prove to be so popular among spectators.
"I don't know really, I'm a horrible person," said the trainer with a smile."The horse is such a professional and very easy to train. He did tread on a stone 10 days ago, which was a bit of a worry, but he was right the next day."
Affection for Sire De Grugy also saturated the words of Jamie Moore as clearly as the sweat which ran off his mount in the winner's enclosure. "I love this horse - apart from my family, he's next best," he said, after a race in which Somerby claimed second place.
The effect of that race would eclipse a day in which Ruby Walsh and Willie Mullins took the opening race at Cheltenham for the second successive day, as Faugheen overcame his rivals in the Neptune Investment Management Novices' Hurdle.
After riding Vautour to a spectacular victory on Tuesday, Walsh showed greater patience on the heavily-backed 6-4 favourite as he settled in third place, before pulling ahead at the second-last bend. Ballyalton moved into second but he could not get anywhere near the four-and-a-half-length winner, while Rathvinden, a stablemate of the Faugheen, finished third. "He looks a bit above average," said Mullins.
Comment would prove harder to get out of Ballyalton's jockey, Will Kennedy, who was banned for three days - March 26-28 - as a result of careless riding. Shane Shortall was also suspended for five days - March 26-30 - for using his whip when out of contention aboard the unplaced Oscars Well in the Coral Cup.
Mullins and Walsh could not, however, book-end the card as Shaneshill finished second to Silver Concorde in the Weatherbys Champion Bumper. Dermot Weld's 16-1 chance ground down the 7-2 favourite inside the final furlong to win by a length and a half under Robbie McNamara, who was recording a first Festival win.
Dai Walters also secured a maiden Festival win when Whisper edged home ahead of Tony McCoy on Get Me Out Of Here in the Coral Cup.
The celebrations were curtailed following Hawk High's win in the Fred Winter Juvenile Handicap Hurdle, though, as news broke of Bryan Cooper's broken leg. He had fallen from Clarcam.
Cross-country specialist Balthazar King, meanwhile, defied top weight to reclaim his crown in the Glenfarclas Handicap Chase.