Thelin had come under pressure earlier in the season, with Aberdeen having taken just one point from their opening six league games and been knocked out of the Premier Sports Cup by Motherwell.
However, an upturn in domestic form gave the former Elfsborg head coach more time.
Aberdeen, who play Rangers in their next two games, finished second bottom of the Conference League league phase with just two points with Thelin winning just eight out of a possible 30 games across all competitions since that Hampden triumph.
Thelin said after Saturday’s loss: “I won’t talk much about the game, but more about ourselves. The desire, there’s too many individual decisions.
“Football is more than technique and systems. It’s how you act on the football pitch. It’s about responsibility. We’ve been here before, we’ve bounced back, but now we’re back some steps again.
“Even if you don’t have the perfect game, it should always feel like we give the fans everything, and right now we aren’t doing that. That’s not good enough.
“I’m the manager, I’m responsible, but sometimes the players have to look in the mirror and know what football is about. We have to drop our egos and play much better as a team.”