Lo Celso steered Betis ahead against Milan
Having scored what proved to be the winner on Betis' trip to San Siro a fortnight ago, the Argentine repeated the trick with just 12 minutes gone on Thursday.
Quique Setien's men showed a patient approach to retain possession before eventually creating the opening they so craved.
Flying flanker Junior Firpo was found in space down the left and rather than flash the ball across the box, he had the presence of mind to pick out a team-mate.
Lo Celso was the man in question as the playmaker swept home first time, finding the far corner with aplomb.