Tidal Bay cruised to an easy victory over Roalco De Farges in the Bet 365 Gold Cup at Sandown.
The Paul Nicholls-trained 9-1 shot, ridden by Daryl Jacob, travelled smartly throughout and pounced after the last for a 15-length win.
The quirky 11-year-old was carrying the top weight of 11st 12 lbs and becomes the oldest winner of the race.
Favourite Le Beau Bai, the Welsh National winner, struggled for pace as Any Currency came home a distant third.
Jacob said: "The horse gave me a great ride. I just sat there and pointed him in the right direction.
"He always travelled well and jumped great. Another fine team effort at Ditcheat.
"I was always fairly confident and he was travelling in his comfort zone.
"I tried to reserve a bit of energy as he had a lot of weight to try to get away from Dickie (Johnson) at the last. He did it well. He got a good jump at the last and got some momentum."
Nicholls said: "When it kept on raining to slow the ground down, it was always going to suit him. We knew they would go that bit slower and it would give him time to get his confidence.
"If it had been quick ground, it might have rushed him and he would not have jumped well enough.
"Everything was right for him today for the first time in a long time."
Bet 365 Gold Cup results:
1 Tidal Bay (D A Jacob) 9-1
2 Roalco De Farges (R Johnson) 7-1
3 Any Currency (Aidan Coleman) 16-1
4 Vic Venturi (J M Maguire) 25-1