The Brazil international replaced Loic Remy after 23 minutes to make his first appearance for the Blues despite signing 63 days prior.
While Ruben Loftus-Cheek opened the scoring shortly after Pato’s emergence, it was the former AC Milan star who grabbed attention, winning and converting a penalty on the stroke of half time.
Chelsea found themselves 3-0 up shortly after the restart when Pato linked up well with Oscar, whose low cross was converted by Pedro.
The Spanish winger added another 13 minutes later when Pato’s shot was saved by Guzan but dropped perfectly for Pedro to knock home.
A disastrous afternoon for Aston Villa got even worse later in the game when Alan Hutton was sent off with five minutes remaining, having earned his second yellow card.