The gap between the top two teams in the league has been closed by Manchester City's victory over the injury-plagued Blues.
The reigning champion struggled in the first half before two of the manager's replacements combined to break the deadlock.
The bottom line is that this defeat leaves them in the unaccustomed position of being 10th in the league.
On a rare night when scoring machine Erling Haaland failed to hit the target, City will be happy to get three points.
The celebrations at the end of the game were a sign that this was a fighting win, which is the hallmark of a champion.
The manager reverted to four in the second half after his side struggled in the first half with three in the middle.
It worked to settle the game as Kepa Arrizabalaga failed to cut out Grealish's cross and the ball went to the other side of the field.
After another outstanding performance, John Stones was honoured by City's travelling fans at the final whistle and the highlight of his performance was a superb tackle on Christian Pulisic in the six-yard box.
The main objective here against a tough opponent was a win that would make up for the disappointing home draw againstEverton and this was very much mission accomplished.
Despite this damaging defeat, the fans applauded their players off at the final whistle as they understood the situation facing the manager.
The club is in transition under new owner Todd Boehly, and the new manager in Potter is trying to put his stamp on the team.
With their outlay and ambition, it's easy to see why they don't look like a contender for a place in the European Championship.
Even though they never lacked heart or effort, they were struggling from the moment they lost their two best players.
Potter's plight was illustrated when he sent on 19-year-old Chukwuemeka for Pulisic and he was joined by three other young men as they tried to save the game.
The ignominy of being replaced late on was suffered by Pierre-Emerick. After a poor performance, he had no reason to complain.
This was more bad news for the club, who now face an uphill battle to get near the clubs they consider their traditional rivals in the league.