The Colin Tizzard-trained Native River hung on to win the 60th running of the Hennessy Gold Cup at Newbury.
The 7-2 favourite crossed the line half-a-length in front of fast-finishing Carole’s Destrier (25-1) with Double Ross (50-1) a gallant third.
It was a first victory in the race for champion jockey Richard Johnson, who had finished second on two occasions.
Earlier, Tizzard’s Cheltenham Gold Cup favourite Thistlecrack cruised to victory in the bet365 Novices’ Chase.
Tizzard is enjoying a golden spell having saddled Cue Card to win last week’s Betfair Chase at Haydock.
Native River appeared to be coasting to a comfortable win in Saturday’s big race before Carole’s Destrier gave him a real fright.
Tizzard said: “It looked like he would win by five lengths, but when Carole’s Destrier nearly got to him, he went again. It is a sign of a good, honest stayer.
“We expected a big run, but he travelled better than ever before and jumped beautifully.”
Analysis on Thistlecrack
Cornelius Lysaght, BBC horse racing correspondent
You may recall there were concerns about Thistlecrack’s jumping being a bit too extravagant, too risky if you like, when he was successful on his second steeplechasing start the other day at Cheltenham.
At Newbury, the horse was nothing short of impeccable. He didn’t put a foot wrong over the 18 fences and the feeling that we are witnessing something remarkable with this horse this season grew markedly.
He is favourite for the Cheltenham Gold Cup and what seemed like an ambitious plan to aim that high this early in his chasing career appears increasingly realistic.