The Denmark midfielder joined Inter Milan from Tottenham for a fee of around £16.9m on Tues.
He came on as a second-half substitute, replacement on-loan Manchester United forward Alexis Sanchez.
Antonio Candreva and Nicolo Barella got the goals for Inter Milan with Martin Caceres scoring for Fiorentina.
Chelsea winger Victor Moses, who joined Inter Milan on loan for the remainder of the season last week, conjointly created an appearance within the half.
Inter will play Napoli within the last four whereas the opposite semi-final sees Juventus withstand AC Milan.