Celtic's Europa League hopes took another blow as Celta Vigo came from behind to inflict their third straight defeat in the competition.
After an emphatic 7-1 win against Hearts, the Hoops once again showed their struggle to take their domestic dominance into European competition. The defeat leaves them as one of four clubs in the 36-team table yet to register any points.
The Celtic fans were screaming for a penalty midway through the first half when Callum Osmond went down from a push from Javi Rueda. It was just outside the box, with the referee deciding not to award a free-kick.
Mika Baur did give them the lead just after the break as he swept home a deflected cross from Haissem Hassan.
After Liam Scales hit the crossbar, Celta hit back with a quick double.
Javi Rodriguez scored twice in three minutes - a header then an unstoppable drive - to stun the home side who could not find a way back as they suffered another damaging Euro night.
Celtic, four points clear of Old Firm rivals Rangers at the top of the Scottish Premiership, face Hibernian at Easter Road on Sunday (kick-off 12pm) - live on Your Site.
12: BLOCK! Colby Donovan is well placed to clear Javi Rueda's cross as Celta Vigo look to open the scoring.
15: BLOCK! Mika Baur is in the right place this time to stop Iago Aspas' effort.
23: PENALTY APPEALS! Callum Osmand is pushed as he ran into the box, but the referee is having none of it. Camilo Duran is booked for his protests.
43: CHANCE! The ball falls to Osmand outside the box after Duran failed to get his shot away. He sends it well over the bar.
44: SAVE! Ferran Jutgla is denied by Sam Johnstone with half time approaching.
47: GOAL CELTIC! Haissem Hassan sends in a dangerous cross, it takes a deflection and breaks to Mika Baur to fire in.
52: CHANCE! Aleix Febas meets Sergio Carreira's low cross only to send it past the post.
63: OFF THE BAR! Liam Scales inches from doubling Celtic's lead. The defender gets his head to Hassan's cross, but it hits the woodwork.
68: GOAL CELTA! Javi Rodriguez meets the free-kick and his header can't be saved by Johnstone.
72: GOAL CELTA! A brilliant strike from Rodriguez, a nightmare for Celtic.They fail to clear the danger and he fires in from outside the box.
85: SAVE! Forrest sets up Donovan, but his effort lacks power and it's easily saved.
Your Site' Luke Shanley was watching at Celtic Park:
Celta were worth their win. The stats don't lie and they had many more chances than Celtic.
The home side were ahead though and what will annoy them is not being able to see it out. Losing two goals in the space of three minutes was a hammer blow.
Martin O'Neill might not be happy with the award of the free-kick that led to the equaliser, but ultimately they needed to defend it better.
Celtic have now lost four European games in a row. The frustration or the worry is that Celtic are not competing enough at this level and can't bridge the gap after winning 7-1 at the weekend in the Scottish Premiership against Hearts.
Their Europa League campaign is all but over but their misery in Europe might not be.
Celtic manager Martin O'Neill:
"Where did it all go wrong? Well, we hit the bar with the header, we could have gone 2-0 in front. I think if we had done that we'd probably have won, but forget ifs, buts and maybes, we conceded a goal from a set piece.
"We just lost a bit of momentum, but conceded the second goal, which was a blinding shot by the player outside the penalty area.
"It was a tough evening, but I can't ask for any more from the players.
"Tonight is disappointing because I thought that we could win the game, I felt that beforehand, and while it was a tight match throughout, I still thought we could win.
"I haven't looked at the table, but I was told roughly that there's still a lot of points to play for.
"We have to obviously win a game at Celtic Park, and we have to win away from home, and I think we're capable of doing that."
