Not for the first time this season, City went on a quick rampage to put the game to bed.
The Sky Blues got their fourth when Gundogan scored with an impressive strike.
Speaking after the game, City manager Pep Guardiola admitted his side had put one foot into the quarter-finals.
"An excellent result," he said. "We are almost in the quarter-finals. Champions League is always 180 minutes and we will take the game seriously but it's an excellent result.
"We are still in February and in the Premier League we are in an amazing position and we are almost in the quarter-finals, we are in one final (EFL Cup) and on Monday we have the opportunity to reach the quarter-finals of the FA Cup. Game by game."