Glasgow City suffered a 2-1 defeat by Anderlecht in the opening game of Champions League Group 3 at Edinburgh's Oriam.
Ella Van Kerkhoven headed Anderlecht in front, before City's Leanne Ross hit the post with a penalty minutes later.
Elke Van Gorp doubled the Belgians' lead when she got beyond the defence to knock the ball past goalkeeper Lee Alexander.
Lara Ivanusa scored a late consolation for City from close range.
It leaves City with a mountain to climb in order to progress, with only the winner of the group guaranteed a place in the last 32 - the stage Glasgow have reached in each of the past three seasons.
City also play FC Martve of Georgia on Friday, who lost 12-0 in their opening game to GKS Gornik Leczna of Poland, who City face on Monday.
City out of their comfort zone
Deposed from their home city due to Glasgow hosting the European Championships, City had set up camp along the M8.
Head coach Scott Booth helped swell the crowd numbers, serving a touchline ban after being sent to the stand in last season's painful last-32 knockout to Kazygurt.
They started the better side without troubling the visitors' goal. Abbi Grant and Leanne Crichton missed the target from close range, before Ross' penalty nightmare came back to haunt her.
It was her spot-kick miss in October last year that proved decisive as City were knocked out by Kazygurt on away goals.
After Anderlecht's Van Gorp had handled in the box, Ross drilled the ball off the post then failed to finish the rebound after goalkeeper Justien Odeurs had pushed it away.
It was a cruel blow, but it summed up City's afternoon - plenty of chances but Odeurs barely having reason to muddy her gloves.
Substitute Jenna Clark passed up a glorious chance at 2-0 down, somehow skewing her shot wide. That proved pivotal, with Ivanusa's finish in added time coming after Kirsty Howat's shot was saved a mere consolation.
The Belgian champions started slow but when they got going they were clinical.
A minute after Stefania Vitafu had fired their first chance over the bar from a free-kick in 24 minutes, Van Kerkhoven could not miss with a near-post header.
That they scored with a header was little surprise. They were taller all over the park, happy to pack their own box and let City aim crosses into their back line.
Sarah Wijnants could have doubled the lead in 57 minutes, Alexander denying her with a great save low down.
Tine De Caigny then should have buried a header when Laura Deloose picked her out unmarked.
But with seven minutes left Van Gorp was able to exploit a gap in the City defence and place the ball beyond Alexander.
Glasgow City head coach Scott Booth: "We're really disappointed. I felt the first 15 to 20 minutes we were quite comfortable, we were the team in possession, but ultimately the moments in the first half where we had the opportunity to hurt them, get shots on target, to use the pressure that we had - we didn't do it.
"We didn't test the goalkeeper once in the game until the very end. We got caught with sucker punches. All in all if you've only had one shot on target then you're not going to win many games.
"Two days is not long enough to recover from a game [City played Celtic on Sunday], but it's not an excuse because I still felt we had periods in that game when we didn't pass the ball well enough or get at them enough. There's a lot of things that we worked on that didn't come into practice.
"I'm disappointed now that it's not in our hands, that we have to rely on Gornik getting a result against them [Anderlecht] and we need to make sure we do our bit by winning our two games."