Big Buck's won his 15th consecutive hurdles race to move within one win of the record for an unbeaten run.
Ridden by Ruby Walsh, he was made to work hard for victory in the Cleeve Hurdle at Cheltenham on Saturday.
The stayer looked in trouble down the hill as Dynaste took the lead, but eventually drew seven lengths clear.
The eight-year-old can now equal Sir Ken's record of 16 straight hurdles wins, set in the 1950s, at the Cheltenham Festival in March.
Dynaste was second and Mourad third in the Cheltenham Festival Trials Day.
Trainer Paul Nicholls said: "He's such a class horse - he gets to the last, pricks his ears and goes.
"Obviously I've left plenty to work on but I just wanted to keep him interested without murdering him at home.
"He switches off in his races. Ruby said he was going to play it late today.
"It's quite a lot of pressure [running him]. I said to [owner] Andy [Stewart] I wanted to run him and he wasn't sure."
The last defeat for Big Buck's came over fences in the 2008 Hennessy Gold Cup when rider Sam Thomas was unseated at the last.
Earlier, Cheltenham specialist Midnight Chase led from start to finish to win the Argento Chase from Tidal Bay.
The victory was the horse's fifth at Prestbury Park.
Tidal Bay, sixth in last year's Gold Cup, provided a late challenge, but Midnight Chase kicked on for the win with Knockara Beau finishing third.
When asked whether Midnight Chase would be put in for the Gold Cup, jockey Dougie Costello said: "Definitely."
Captain Chris, who was third in last month's King George VI Chase, was pulled up early in the race after continually jumping out to the right.