Somersby dug deep for rider Dominic Elsworth to beat Finian's Rainbow and win the Victor Chandler Chase at Ascot.
The 9-2 chance, saddled by Best Mate's trainer Henrietta Knight, stayed on well for a first Grade One success.
Al Ferof was third and Gauvain fell as last year's runner-up triumphed in the 25th anniversary of the race.
According to Pete (9-1) won the Peter Marsh Chase at Haydock while trainer Donald McCain and jockey Jason Maguire enjoyed a four-timer.
Wearing cheekpieces for the first time, Somersby went one better than his narrow defeat by Master Minded in 2011.
The eight-year-old, who was fourth behind winner Kauto Star in the King George VI Chase at Kempton on Boxing Day, had previously finished second in two Grade One and three Grade One chases during his career.
Somersby overhauled Finian's Rainbow in the run-in to claim victory by a length-and-a-quarter and provide Knight with her first top-level success since 2005.
Her partner Terry Biddlecombe, the former champion jockey who is recovering from a recent stroke, was on hand to see the triumph.
"I got so excited, I had a nosebleed," he said.
Elsworth said of Somersby: "I'm delighted for the horse. He's been a bit of a bridesmaid, but he's done it nicely. I always knew he was going to stay on towards the end."
Knight indicated the Ryanair Chase at the Cheltenham Festival in March would be his target, although the Queen Mother Champion Chase is an alternative.
At Haydock, the 11-year-old According To Pete saw off younger rivals for a stamina-laden success.
Celestial Halo (6-5 favourite) continued his revival by winning the Champion Hurdle Trial for trainer Paul Nicholls.
Meanwhile, McCain and Maguire chalked up victories with Cinders and Ashes, Our Mick, Reindeer Dippin and Real Milan.