The French side had chances of their own with Henri Saivet shooting just wide and Romain Hamouma firing over in the first half, while Nolan Roux nearly levelled on 73 minutes with a delicate chip.
"Every time I've played against Saint-Etienne, with luck or with a good performance, there have been a couple of goals!"
"I know Champions League is a competition that everyone wants to play and win but we don't play Champions League; we play Europa League", he reflected.
Ibrahimovic loved playing against Les Verts throughout his four years at Paris Saint-Germain so perhaps it was inevitable that the Swede should be the difference between the teams at Old Trafford.
Knowing one goal might not be enough ahead of the reverse fixture, United ran riot in the second half and were rewarded with a brilliant goal when Zlatan's got his 2nd goal of the night against the visitors in the 75th minute.
Ibrahimovic's deflected free-kick wrong-footed goalkeeper Stephane Ruffier and dribbled over the line for the opener, and he tapped home from close range after good work from Marcus Rashford, as well as adding a late penalty.
The sides previously met in the European Cup Winners' Cup first round in 1977, but the second leg was played at Plymouth Argyle on England's south coast after crowd trouble marred the first leg. I always respect football and I know football can be nasty to you, so I go with a strong team.
Ibrahimovic, 35, took his tally of goals against Saint-Etienne to 17 in 14 games, but the 17th hat-trick of his career was also probably the most scruffy. "Tonight in the first half, it was too relaxed".
Saint-Etienne go into the game on the back of a breezy 4-0 win over Ligue 1's bottom club Lorient, which defender Kevin Malcuit believes was helpful preparation. Everything can change quickly, but we're happy at the moment and working hard.
Thursday's victory keeps United on track for continental glory, with Jose Mourinho's men still in the race for the EFL Cup and FA Cup as well.
"To score three goals, not concede at home, it's a good result".