The only goal of the match booked a clash in the last four against Wolves or Sevilla.
And Solskjaer revealed Fernandes altered his trademark skip in his run-up because goalkeepers have starter to study his style.
“He knows that keepers will wait for him to do the jump,” said the United manager.
"“He practices both of them and he practices both sides so he’s got them sorted. He’s better than I was anyway!”
— Football on BT Sport #Club2020 (@btsportfootball)August 10, 2020
It was Fernandes’ 11th goal 20 appearances since his January move from Sporting Lisbon.
That it required a penalty to see off a stubborn Copenhagen, who had an inspired keeper in Karl-Johan Johnsson, underlines just how stern a test United were given in the quarter-final in Cologne.
Solskjaer told BT Sport: “I thought we deserved to win tonight. Their keeper was fantastic. He was unbelievable.
“We hit the post a few times, there were a couple of offside decisions against us, VAR. It could have been one of those nights that you end up with a penalty shootout.
“It was about patience, not making mistakes, don’t give them opportunities that we don’t have to, let them earn their chances and we knew we’d create chances.
"Anthony, Marcus, Bruno, Paul will always create chances in every game.”