Clan Des Obeaux and Harry Cobden finished strongly to secure a 10th King George VI Chase win for trainer Paul Nicholls at Kempton.
The horse, part owned by Sir Alex Ferguson, battled with veteran Thistlecrack from the home turn.
But a strong jump from the 12-1 shot at the last fence saw him pull clear of his rival.
He powered on to win by a length and a half with Gold Cup winner Native River back in third.
Clan des Obeaux had looked less than impressive in his last outing at the Betfair Chase at Haydock but at only six years of age, Nicholls was always confident he would get better with more experience.
Former Gold Cup winner Coneygree had shown plenty of spirit early on with Might Bite also prominent and Thistlecrack keeping in touch with the leaders too.
There was drama as they embarked on the second circuit when Bristol De Mai parted company with Daryl Jacob and brought down the Ruth Jefferson-trained Waiting Patiently and jockey Brian Hughes in the process.
Thistlecrack looked strong as he took the lead but Cobden had a patient ride on Clan Des Obeaux, four years younger than his rival, and the pair showed their strength when it mattered to claim a famous win.
Source BBC News