Oblak produced a man-of-the-match display with a number of important saves in Atletico's stunning 3-2 extra-time victory over Liverpool at Anfield on Wednesday.
Liverpool were on top for much of the last-16 second leg - having 34 shots on goal - but they could not move clear of Atletico or get the better of Oblak as the visitors secured a 4-2 aggregate triumph thanks to Marcos Llorente's brace and Alvaro Morata's late strike.
Regarded as one of the world's best goalkeepers, Oblak earned high praise from Atletico head coach Simeone post-match.
"We have a goalkeeper who is the best in the world, no doubt," Simeone said. "I have been saying that for some time.
"It's like Barcelona who have Messi. He decides games with his attacking play; Oblak resolves them with his saves."
Llorente came off the bench to replace a frustrated Diego Costa and Simeone added: "Llorente revolutionised the team.
"I'm very happy for the team and the club. It was a historic match against an extraordinary opponent with great intensity and a beautiful stadium.
"They pushed and held, without us ever moving away from our plan and with everyone's effort we succeeded.
"It gives me an enormous joy because, although it seems simple, it's not simple to win."
Atletico's English international Kieran Trippier explained it was important for the Spaniards to stay resolute before taking their chances on the counter.
"We knew it was going to be very difficult, even with the lead. Liverpool are a fantastic side," Trippier told BT Sport.
"We needed to stay defensively strong, keep our shape and frustrate Liverpool.
"We knew we would get our chance to break the press of Firmino, [Sadio] Mane and [Mohamed] Salah.
"We kept going and we got the win. We knew we'd get our chances and it's just about being clinical in those moments."