The eight-year-old gelding travelled strongly throughout the race, jumping cleanly under a positive ride from Noel Fehily.
The pair led from the start, mostly tracked by Champagne Fever, who tired towards the end under Ruby Walsh, to finish fourth.
Silviniaco Conti won by 4 1/2 lengths from David Pipe’s Dynaste in second, ridden by Tom Scudamore. A further 5l back in third was another Nicholls horse, Al Ferof, who also finished third in the 2013 race.
“He’s a hell of a good horse,” said Fehily of Silviniaco Conti. “He proved today what a good horse he is whatever the ground, he’s gone a good gallop the whole way.”
Silviniaco Conti, who was sent off 15-8 favourite, jumped boldly and had a good rhythm for the whole three miles. He now heads to the Cheltenham Gold Cup, although Nicholls has not yet decided whether the gelding will have another run between now and March.
“He was really good today, he’s a much improved horse and we now look forward to Cheltenham.
““He gallops and stays and he’s very fit,” said Nicholls — who also won the King George five times with Kauto Star and twice with See More Business.
Dynaste put in a solid performance under Tom Scudamore. Tom had earlier in the day won at Wincanton on Batavir, and had arrived at Kempton in a helicopter in order to take part in the feature race.
Al Ferof ran on strongly for Sam Twiston-Davies for third, and the grey, who runs in the yellow, white and red silks of John Hales, owner of Nick Skelton’s showjumping star Arko, may now head to the Champion Chase at Cheltenham.
Cue Card came home fifth, Johns Spirit was sixth, Wonderful Charm was seventh.
Menorah made a bad error on the way home, finishing eighth, while Philip Hobbs’ other charge Wishfull Thinking pulled up.
Earlier in the day Coneygree, trained by Mark Bradstock, provided jockey Nico de Boinville with his first Grade One win in a drama-packed Kauto Star Novices’ Chase,
Favourite Saphir Du Rheu fell, as did Sausalito Sunrise, while Creepy pulled up and Carraig Mor unseated Noel Fehily.
Meanwhile, Faugheen put in an outstanding performance in the williamhill.com Christmas Hurdle winning by 8l to Purple Bay and confirming his position as favourite for March’s Champion Hurdle.