The Argentine scored twice and set up another as United's losing run stretched to seven.
Como handed Manchester United a 4-1 thrashing in the Champions League league phase at the Stadio Giuseppe Sinigaglia on Wednesday.
Nico Paz scored inside two minutes and added a second, while also setting up Tasos Douvikas. Jacobo Ramon completed the scoring for the Italian side before Joshua Zirkzee pulled one back for United in stoppage time.
United arrived on a six-game losing run, and injuries and suspensions forced manager Michael Carrick to field a weakened defence. The visitors became the first English team to concede within the opening two minutes in successive European matches.
Paz became the second-youngest Argentine to score against United in the competition, behind only Lionel Messi.
