Don Poli ended top Irish trainer Willie Mullins' long wait for a Lexus Chase triumph as he held off First Lieutenant to win the Grade One Leopardstown race.
The 4-6 favourite, an impressive winner of last season's Cheltenham Novice Chase, had to work hard to hold off the 16-1 runner-up by half a length.
Foxrock (10-1) was a further half a length back after an exciting finish.
Jockey Bryan Cooper allowed Don Poli to drift on the run-in but a stewards' inquiry left the result unchanged.
The stewards checked whether Don Poli's edging towards the rails had hampered the Ted Walsh-trained Foxrock but the placings remained unaltered.
Despite his domination of Irish National Hunt racing, Mullins had never won the Christmas Leopardstown highlight, but he had a three-strong challenge in Monday's six-runner field as he also saddled On His Own and Sir Des Champs.
On His Own cut out much of the running in the soft conditions with the help of Foxrock but Don Poli closed right up on that pair approaching the final fence.
As On His Own weakened and Don Poli forged ahead, veteran First Lieutenant began to stay on in the hands of Davy Russell.
Running in the race for the fourth time, it briefly looked as if First Lieutenant might catch the favourite but the line came just in time for Cooper's mount.
Bookmakers Paddy Power were not impressed and pushed Don Poli out from 4-1 to 6-1 for the Cheltenham Gold Cup in March.
Mullins happy despite tight finish
Mullins' second favourite St Des Champs was never a factor as he finished a distant fifth but the trainer was content after breaking his duck in the Leopardstown race.
"It's hard to know how good he (Don Poli) is and how much more he has to produce but I was very happy," said Mullins.
"Bryan said he thought he was in trouble going to the last but he picked up again when they came and went on again."