Sprinter Sacre's absence had made this an immeasurably easier task, but the tricky fences along the back straight still stood in their way and Moore's son Jamie was put to the test.
However, Sire De Grugy's tremendous determination prevented him from being boxed in on the tight run around the last couple of fences and a storming leap at the last gave him enough breathing space to thwart the staying-on Somersby by four lengths.
A typically inexpensive purchase by the Moore family, the 7-4 favourite was given a great welcome from a crowd appreciative of a major victory for one of the less fashionable combinations.
Moore senior said: "It just goes to show it doesn't matter what you pay for them, it doesn't always make them. A lot of top people passed him over, but a lot of credit must go to Jamie, as he went and saw him and said 'you've got to buy this horse as soon as you can'."
Sprinter Sacre could make his belated reappearance in the Desert Orchid Chase at Kempton over Christmas, and Moore believes it would be his only chance of beating the National Hunt great. He said: "I'm going to have to take him on at some point and I'd rather it was at Kempton [Desert Orchid Chase, December 27]. If I want to swerve him I can go to Leopardstown, but I'd say he'll go to Kempton.
"He won't necessarily go to Cheltenham as I think he needs a more conventional track, but I'd like to take him to France at some stage."
His son, for once stealing the spotlight from brother Ryan, said: "I'm delighted for my dad. It is my best achievement, there was a bit of pressure as we love him to pieces. He just jumped a little bit left at a couple down the back, I don't know why, but that's where the ground is at its quickest and he probably does want a bit of dig in the ground."
Paul Nicholls sent out five winners across the country, with the biggest of them a Daryl Jacob-ridden Esher treble coming through Hinterland (13-2) in the Racing Post Henry VIII Novices' Chase.
Nicholls' Saphir Du Rheu (8-1) bolted up in the Pertemps Network Handicap Hurdle, while There's No Panic (9-1) rounded off a terrific day at the Ditcheat office in the LDS Leak Detection Specialists London National.
At Aintree, Chance Du Roy repelled the sustained challenge of admirable teenager Baby Run in a pulsating climax to the Betfred Becher Chase.
The 13-year-old Baby Run, a winner over the famous fences in the 2011 Fox Hunters' Chase, was making his first competitive appearance since finishing third in the bet365 Gold Cup at Sandown just weeks after those Aintree heroics two years ago.
Despite his advancing years, the veteran jumped beautifully under Sam Twiston-Davies and was still there rounding the home turn.
The Philip Hobbs-trained Chance Du Roy, making his first start since the spring, came to claim the veteran after jumping the final fence and looked ready to assert, but Baby Run drew reserves deep from within to have another go on the famous run-in.
The neutrals roared as the old timer closed the gap, but to his credit, Chance Du Roy went again under Tom O'Brien and held on to score by a length. Mr Moonshine, carrying the colours of last season's Grand National hero Auroras Encore, finished third, ahead of Ballybough Gorta in fourth.
Sarah Hobbs, wife of the winning trainer, said: "He loves this course. He stayed on really well at the finish and you'd like to think he could maybe come back here in April for the National, although I think there'll be a bit of opposition from the owner.
"When Planet Of Sound was a non-runner [because of the ground], Tom offered the ride to Richard [Johnson, stable jockey] but Richard said Tom knows the horse better so let him keep the ride, which was nice."