Altior has suffered his first defeat over jumps with Cyrname a brilliant all-the-way winner in the Christy 1965 Chase at Ascot.
Unbeaten in 19 previous starts over hurdles and fences combined, The Nicky Henderson-trained Altior was all the rage to make it 20 as the 1-3 favourite to win beyond two miles (3200m) for the first time.
The Paul Nicholls-trained Cyrname ended last season as the highest-rated steeplechaser in Britain - 1lb above Altior - following two wide-margin wins over the 4200m at Ascot but was relatively easy to back at 5-2.
With the only other runner Solomon Grey never a factor, it was a two-horse race from the start with Harry Cobden sending Cyrname straight to the lead and Nico de Boinville sitting on his tail aboard Altior.
As the pace increased down the back straight, it was Cyrname who produced the slicker leaps.
Altior did his best to bridge the gap in the straight, but Cyrname refused to give up and a flying jump at the final fence sealed a 2-1/4 length success.
"I'm very proud of him and the whole team, who have played a big part in getting him right and getting him mentally right," Nicholls told Sky Sports Racing.
"He was very nearly unmanageable at home and on the course, then all of a sudden the penny dropped.
"He started to believe in us and mature. Now we've got a horse who is the finished article.
"It was always going to be about stamina and three miles won't be a problem to him."
Paddy Power cut Cyrname to 5-2 favourite from 9-2 for the King George VI Chase at Kempton.
Whether Altior turns up on Boxing Day for the rematch remains to be seen, with Henderson keen to let the dust settle before committing to future targets.
"He has run a very good race. He has done exactly what we all expected to happen and he had a go at him. To be fair, he has got very tired," he said.