The victory over AC Milan was an emphatic one for the Blues in their first game of the season.
After a poor start to their group phase with a defeat away to Dinamo Zagreb and a draw at home to Red Bull Salzburg, Graham Potter knew victory was needed.
The English right-back was the star of the show, as they eventually defeated Milan.
The defender scored his first goal for the club after 24 minutes when Milan failed to clear a corner, but his night was ended by an injury.
The Italians had a chance to tie the game at the half-time break, but Krunic missed the goal.
It was a rare anxious moment in the second half and James in particular, the right-back, demonstrated why he commands such faith at club level.
James was the provider after 56 minutes when he crossed for Pierre-Emerick Aubameyang to apply a simple finish, then five minutes later he was the goal scorer with a powerful strike which flew high past Milan's keeper.
There is more to come.