Felix became the fourth most expensive player of all time when he joined Atletico Madrid for €126 million from Benfica in 2019.
This defeat means that Chelsea has now conceded in all of their last six fixtures across all competitions.
Manuel Akanji moved to Man City after agreeing a five-year deal to leave Borussia Dortmund.
A close-range header in the first half was Aubameyang’s 11th goal in his past 14 games for Barca.
In-form Barca sit second, 12 points behind leaders Real Madrid but with a game in hand and eight to play.
Real Madrid are still first on La Liga log with 66 points in 29 games. Sevilla is second with 57 points in 29 games, while Barcelona are third with 54 points in 28 games.
Spanish side Barcelona booked their place in the round of 16 of the Europa League, beating Napoli 4-2 win on Thursday.
Barcelona are now fourth on the log with 42 points from 24 games while Valencia are 12th, ten points above the relegation zone.
New Barcelona striker Pierre-Emerick Aubameyang has aimed a subtle dig at his former manager, Mikel Arteta, claiming he was “the problem” at Arsenal.
Aubameyang will join the Spanish giant for free, despite having 18-months left on his contract with Arsenal.