Oblak produced a fine display that included a spectacular triple-save early in the second half to deny Julian Brandt and Kevin Volland, as Atleti delivered a disciplined performance that ensured their aggregate lead rarely looked under threat.
The Slovenia international was somewhat frustrated not to win the game but believes last season's beaten finalists deserve credit for reaching the last eight once again.
"We feel very good," he told BeIN Sport. "Atletico are in the quarter-finals for the fourth year in a row and it's very important for the club.
"We fought to win. It didn't turn out like that but the important thing is to be in the quarters.
"Of course, it's not easy to be in the best eight teams in Europe for four years. I hope we keep improving and keep achieving big things."
The draw for the next round takes place on Friday in Nyon.