Oblak was in the thick of the action, producing a world-class save to stop Sebastian Coates and denied Bryan Ruiz twice, though he was at fault for Fredy Montero's winner.
However, Atletico midfielder Koke was full of praise for the Slovenia international, who has been linked with Liverpool and Paris Saint-Germain previously and has admitted uncertainty over his future at the club.
"Jan has us used to matches like that, with high-level games," Koke told beIN SPORTS.
"I hope he stays that way until the end of the season. I would give Oblak a blank cheque."
On the match itself, Koke added: "We had difficulties because the opponent played a great game, especially in the first half, but we are happy with the qualification for the semi-finals.
"It is not easy, we have seen this week in the Champions League and we are in the semi-finals, which was the goal."