City lost 2-1 to Brighton after taking a 0-1 lead.
Pep hadn't won a single match in his last three matches under Brighton manager Fabian Hürzeler.
City started well, but Haaland missed a goal opportunity in the 9th minute. A poor shot wasted a potential goal.
Milner celebrated his goal six years later at the age of 39.
City played poorly after conceding the equalizer. They couldn't mount a proper attack. Brighton took a 2-1 lead in the 89th minute through Gruda, who secured a victory.
City suffered their second defeat in their third match.
Something had been wrong at City since last year. The problem lies in Pep's appointment as manager.