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Funnell's tense Hickstead jump-off
Will Funnell and Cortaflex Mondriaan triumphed in a thrilling jump-off to win the DFS British Jumping Derby.
Geoff Billington and Funnell were the last riders out, and the two former winners matched each other for experience and professionalism.
But Funnell's clear round in the jump-off at Hickstead was too much for Billington and Cassabachus.
"Geoff pushed me to the wire but Mondriaan jumped fantastically, he deserves it," Funnell told BBC Sport.
Funnell, husband of Olympic eventing silver medallist Pippa, has now twice won the Derby, having done the same with Mondriaan in 2006.
"After a disappointing set of first rounds it was a day for Derby specialists," said Lizzie Greenwood-Hughes, BBC Radio 5 Live's equestrian reporter.
"It was a popular win here - Will and Pippa are based not far away from Hickstead, in Dorking."
Billington matched Funnell's four-fault round under intense pressure to take the Derby to an extra duel, and looked good to equal Funnell's faultless outing in the jump-off.
But Cassabachus - 2007 winner alongside Billington - lowered the eighth fence of lightly balanced planks, known as the Derby rails, to hand Funnell victory.
"Mondriaan is 14, he's very sound and now that I'm not doing any more Nations Cups I'll lay him out every year and save him for the Derby," said Funnell, from Ockley in Surrey.
"The crowd here cheer you and the whole atmosphere of Hickstead can't be compared to anywhere in the world."