The 29-year-old had a chance from the spot kick to help the Gunners claim the maximum points against Tottenham Hotspur but saw his effort saved by goalkeeper Hugo Lloris.
Against the Red Devils, the former Borussia Dortmund player made amends when he calmly slotted his kick to seal the victory for the Gunners after Alexandre Lacazette was brought down in the box.
And the forward has explained that his concentration helped him avoid a repeat of the mistake at Tottenham.
"I was confident, my team-mates give me a lot of confidence. Laca gave me the penalty and that was cool from him, I was really focused,” Aubameyang said on Sky Sports.
“I made a mistake against Tottenham, looking down at the last moment, not watching [Hugo] Lloris, but today I watched until the end and being focused you score a penalty.
"I know where the ball is and you have to practice this all the time, and today it went in! I knew that it would be tough, but I was feeling confident and if I missed this one, what can I say?"
The victory saw Unai Emery’s men return to Premier League top four after gathering 60 points from 30 games.