Liverpool suffered the biggest upset of the group stages so far as they slipped up 2-0 to Red Star Belgrade.
Jurgen Klopp joked afterwards that he didn't have enough hands to put his finger on what went wrong as part-time electrician Milan Pavkov scored a brace.
Perhaps the intensity or the sheer terror of playing at a raucous Rajko Mitic Stadium got to his side.
It was a worrying indication that last year's finalists might not be up to the same level in Europe this time around - but, on the flip side, what a result for Crvena Zvezda.
Red Star, of course, are back in the Champions League after 26 years, a competition that gave them their most famous night in 1991 before the team broke up as a result of the Yugoslav wars.
A little more recently, in 2014, they were expelled by UEFA over Financial Fair Play breaches,
These are no minnows, in the history of European football, but many had them as high as 80/1 to beat the Reds. It's still a phenomenal achievement that has left the five-time winners reeling.
Liverpool fans' spied Markovic liking a tweet
Well, most of them anyway. Those who still bother to follow fringe player Lazar Markovic were not too happy with the winger after he liked a tweet comprised of Serbian flags after the final whistle.
Nobody would blame the 24-year-old for being a little disgruntled at the way his Anfield career has panned out, but it still seemed a highly unprofessional thing to do.
Thankfully, Markovic has now clarified why he liked the tweet - even though it was posted by Youtuber David Vujanic, who appears to be a Red Star fan.
Markovic has explained
"Dear people, I made "like" to the picture with Serbian flags," Markovic explained.
"I'm an ex Partizan Belgrade player and big supporter. As such obviously I couldn’t jump around celebrating Red Star Belgrade winning the match. Specially not against @LFC. Thank you all!"
Markovic very rarely comes to the attention of Liverpool fans these days.
Since the £20million man's arrival, he has been on loan to Fenerbahce, Sporting Lisbon, Hull City, and Anderlecht, though making little impact in any of those spells.
In pre-season, Klopp gave him one last chance to put himself in the shop window but while he actually scored against Blackburn, nobody came in for him.
All in all, he hasn't done much to endear himself and despite his explanation, his social media activity isn't likely to have helped his case.
What do you make of Markovic's tweet? Have your say in the comments.