However, trainer Nigel Twiston-Davies insisted the second-placed Imperial Commander is still on course for a Gold Cup outing on March 15.
The feature event on a glittering card almost provided the dream outcome for local hero Imperial Commander, the 2010 Gold Cup winner, who had been sidelined for nearly two years by various ailments.
The veteran showed his old vigour as he tore through the final circuit and opponents dropped gradually away, but O'Regan shadowed Paddy Brennan, redoubling his efforts after Cape Tribulation (7-1) jumped sloppily in the home straight, and summoned half a length extra in a memorable finish to one of the key Gold Cup trials.
Cape Tribulation's trainer Malcolm Jefferson said: "Now I think we will probably have to come back for the Gold Cup. I'm not saying he's going to win it but he might get placed in one, this year's especially. He's in the World Hurdle, but he is jumping so well now I think the Gold Cup is the race he'll go for.
"On his day he's a good horse. He might be better on better ground and if could get a place in the Gold Cup that might be better than running with a big weight in a handicap."
Nigel Twiston-Davies was rightly full of praise for Imperial Commander (7-2). "You'd have to be delighted and if we'd been able to get him fit enough he prob-ably would have won," he said. "It's been so difficult getting him back with his splint problems, but we have kept him swimming and that made all the difference.
"He kept tanking and if he had settled better he would probably have had more of a finishing kick. There's six weeks to go for the Gold Cup and that is plenty of time."
Third home Hunt Ball travelled as well as anything for a long way before his stamina ran out on the ground, and his trainer, Keiran Burke, also confirmed a Gold Cup bid was in the offing.
He said: "We were going to go for the Racing Plus Chase, but I think we will give that a swerve and go straight to the Gold Cup. He'll get the trip on better ground."
David Pipe had no explanation for the run of favourite Grands Crus, who dropped away as tamely as he had in the Paddy Power Gold Cup earlier in the season.
Meanwhile, Sprinter Sacre showed once again why he is dubbed the "Frankel of the jumps" as he completed a magnificent seven over fences with a majestic display in the Victor Chandler Chase. Not for the first time, Nicky Henderson's superstar was electric at his fences, taking up the running on the way to the sixth-last, after Mad Moose had opened a sizeable early advantage.
Barry Geraghty quickened matters noticeably going to three out and while Sanctuaire had crept into it from the rear, his threat was only a fleeting one as Sprinter Sacre sauntered over the last two fences. The gallant Mad Moose rallied as Sanctuaire began to toil, and got up past Somersby to take second, some 14 lengths adrift of the 1-5 favourite.
Henderson admitted: "I'm glad it's over. I had reservations about running, but we had to. Barry was worried about the ground, I was worried he was a bit fresh. He can handle any ground, I think, and that's what a good horse should be able to do.
"Barry's confidence in him is unbelievable. He knows you can jump anything with him. He's such a gorgeous horse to look at, you would think he would be something special. He knows he is special and I suppose we are all starting to believe he might be."
Sprinter Sacre is now expected to head straight for the Queen Mother Champion Chase in March, for which he is 1-3 favourite with Ladbrokes. Henderson said: "It is a shame to be going to Cheltenham as his third run of the season, but that's the sort of season it's been."
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