Chelsea had granted dispensation for both Mount and Tomori, who are spending the season on loan with Frank Lampard's team, to play against their parent club on Wednesday night.
Tomori scored an unfortunate own goal early on but performed well thereafter, while Mount once again showed his class following a fine start to the season.
Mount was called up to the England squad by Gareth Southgate last month.
"He [Tomori] was unlucky with the own goal, but the performance he and [Richard] Keogh put on afterwards was excellent," said Zola after the game.
"It happens. If he hadn't touched the ball, [Alvaro] Morata would have scored a goal. He played well.
"Mason Mount played excellent. It looks like they're in good hands. They're doing very well for the team. The coaching they're getting is excellent."