The chestnut filly is as short as 10-1 for the Newmarket Classic after her Group One success, and is only behind stablemate Flashy Wings, who took the Lowther Stakes at York.
Eoghan O’Neill’s Always Hopeful made most of the running before the Aidan O’Brien-trained favourite Ivan Denisovich took over with around two furlongs to run.
But Silca’s Sister, ridden by Ted Durcan and sent off at an industry price of 9-1, was also travelling well on the rain-softened surface and quickly threw down the gauntlet.
She ran out a decisive winner in the final furlong, scoring by two lengths from Ivan Denisovich with a nose back to Always Hopeful in third.
Domestic challenger New Girlfriend, trained by Robert Collet, had been highly-touted having impressed in both her previous starts and she briefly looked dangerous but failed to quicken at the business end of the race.
Channon’s other runner Puskas failed to figure, but the trainer, who was winning his first Morny, said: “We always thought she was a good filly, and this proves that she’s very good. I wasn’t that nervous before the race, I let my horses do the talking.
“I’ve got some very decent fillies this season, with the likes of Flashy Wings.
“It was a big test for Silca’s Sister today. We were a bit concerned about the soft ground, but she coped with it fine.”
Silca’s Sister had taken a Newbury maiden on her previous start, but when asked if it had been a risk bringing her over Channon replied: “A lot of winners have come out of that race so we didn’t think it was too big a gamble.”
Silca’s Sister was completing some unfinished family business as her sister, Golden Silca, finished third to Orpen in 1998.
William Hill slashed her Guineas odds to 11-1 from 25-1, Ladbrokes went 14-1 from 20-1, Coral 14-1 from 33-1, Cashmans 12-1 from 33-1, while VC Bet and Paddy Power both cut her to 10-1 from 25-1.
Flashy Wings is a general 7-1 favourite.
“Channon’s hit the crossbar a couple of times in the past with the likes of Bint Allayl and Queen’s Logic so hopefully it’s a case of third time lucky this time around,” said Balthazar Fabricius, of Ladbrokes.
Further British success came when Hughie Morrison’s Alcazar claimed the Group Two Darley Prix Kergorlay at the ripe old age of 10.
Mr Vegas led early on in the mile and seven furlong marathon before Ostankino took over and maintained the advantage until the home turn where he was collared by Alcazar, who was swinging along for Michael Fenton.
The pair matched strides for about a furlong before Alcazar imposed his authority on the race and held on for a clear-cut two-length verdict.
Favourite Reefscape had dropped back to nearly last with two furlongs to run before finishing with a wet sail to take second by a neck ahead of Ostankino, while Mr Vegas was eventually a tailed-off last.
Alcazar, returned at an industry price of 6-1, had to survive a stewards enquiry after it looked like he had interfered with Ostankino, but the placings remained unaltered.
Cassydora made a bold bid to land the Darley Prix de la Nonette but was thwarted as domestic challenger Viane Rose landed the spoils.
Kerrin McEvoy set the pace for the first half of the 10-furlong Group Three aboard John Dunlop’s filly, a winner of the Lingfield Oaks trial earlier in the season, but she was headed turning for home.
Barry Hills’ Alumni led briefly in the straight but was soon challenged on the inside by Viane Rose, trained by Jean-Claude Rouget and ridden by Ioritz Mendizabal.
She swept to victory by half a length, holding the late challenge of Spectrofolle while Cassydora found a second wind to finish a head back in third.
Rouget was all smiles with Viane Rose’s win, 24 hours on from his one-two in Saturday’s Prix Guillaume d’Ornano with Pinson and Ruwi.
“She was in season the last time she ran at Chantilly,” he said.
“This win proves she’s right up there with the best fillies. She appreciated the soft going.”
Mendizabal added: “We weren’t absolutely certain she’d stay the trip so I was careful not to produce her to the front too early. This has given me a lot of pleasure.”
The other British raider Joint Aspiration briefly looked dangerous but finished last while Karen’s Caper was a non-runner.
Christophe Lemaire delivered Pride with a well-timed run to defy Sir Michael Stoute’s Red Bloom close home in the Prix Jean Romanet.
Kieren Fallon had dictated the pace aboard Red Bloom and turning into the home straight it looked like he might have stolen the race.
Although Pride was a few lengths adrift, she picked up nicely and won by three-quarters of a length, with a bit more in hand.
Trained by Alain de Royer-Dupre, the five-year-old was reversing placings with third-placed Whortleberry, who beat her in the Group Two race last year.
Lemaire said: “She came with plenty in hand to pass Red Bloom and I wouldn’t be surprised to see her winning a Group One soon. She’s a filly with a lot of class.”