The Red Devils needed the help of the much maligned Cameroon goalkeeper to come to their aid in second half stoppage time to preserve their 1-0 advantage and he duly responded by palming away Jordan Larsson's effort which was virtually the last kick of the game.
Onana has delivered some error-strewn performances since making the switch from Inter Milan this summer but on this occasion did enough to hold his own.
The late save breathed some life back into Manchester United's Champions League hopes which were fading after two successive losses.
On a night riding on the redemption theme, it was Harry Maguire who scored the only goal of the game.
“He showed personality and he knows that before was not the levels what his skills are,” manager Ten Hag said of the former Ajax Amsterdam goalkeeper.
“He didn’t match his skills and he could do better.
“I think Saturday (against Sheffield United) was a very good performance and today as well.
“Also, don’t forget that brilliant save just after half-time in the counter-attack.
“But, of course, that is one of his skills, he is a very good penalty saver.”
Manchester United will return for the second leg in Denmark on November 8.
