Theatre Guide opened his account for the campaign after snatching a last-gasp victory in the Unicoin Group Handicap Chase at Cheltenham.
Despite failing to feature in last month's Hennessy Gold Cup, the nine-year-old showed his appetite for a thorough stamina test when getting up on the line to take the Grade Three contest and score for the first time since February.
Approaching the final fence, the Colin Tizzard-trained 15-2 chance looked booked for third as stablemate Bally Longford powered into what appeared a race-winning advantage.
That lead was soon reduced up the hill as both Theatre Guide and long-time leader Perfect Candidate forged on to fight out the finish, with one last lunge seeing Paddy Brennan's mount prevail by a nose.
The winner was trimmed into 20-1 from 25-1 for the Welsh National by William Hill.
Tizzard said: "He just showed he is a thorough stayer. We were disappointed he didn't stay on in the Hennessy, as that's what he does best.
"That was lovely for Jean (Bishop, owner) and my daughter rides him every day. We just felt he didn't go through with the job in the Hennessy.
"Whether it was because it was a higher-class race I don't know, but he definitely went through with it today to the line.
"He is thorough stayer and that (Welsh National) looks the obvious race for him."
As well as the agony of such a narrow defeat, there was an additional sting in the tail for Conor Shoemark, rider of Perfect Candidate, as he was hit with a 15-day suspension by the stewards for using his whip above the permitted level, without giving his mount time to respond and in the incorrect place.
He will sit out December 26 to January 9 inclusive.