Ole Gunnar Solskjaer masterminded Manchester United's 2-1 league win at neighbours City earlier this month but he says they will have to produce something different if they are to get the better of them again in the League Cup semi-finals.
United's superb counter-attacking display left City's Premier League title defence in tatters on Dec. 7.
The Norwegian expects Pep Guardiola's side to be a different proposition when they meet on Cup duty in January.
United powered past fourth-tier Colchester United 3-0 in the quarter-finals on Wednesday while holders City stayed on course to lift the trophy for a third straight season after overcoming third-tier Oxford United 3-1.
"You won't beat City twice in a row or three times with the same tactics, so we'll have to do something better than we did last time because I'm sure Pep will have his team fired up," Solskjaer told reporters.