Celtic manager Brendan Rodgers said his side showed they can compete in the Champions League after a 2-2 draw against Atletico Madrid on Wednesday, despite failing to end a decade-long wait for a home win in the competition.
The Scottish champions twice led through Kyogo Furuhashi and Luis Palma, but were pegged back by Antoine Griezmann and Alvaro Morata.
Atletico then had Rodrigo De Paul sent off in the closing stages.
Celtic, though, could not make the man advantage count in the final eight minutes plus stoppage time to leave their chances of progressing in Group E looking slim.
A draw takes Atletico to within a point of group leaders Feyenoord, who beat Lazio 3-1 on Wednesday.
Celtic's first point in the group leaves Rodgers' men three points adrift of the third-placed Italians.
"We showed we can compete with a top level team," said Rodgers. "I don't think you can say they'll fly back to Spain not knowing they've had a tough game.
"The performance gives you the confidence at this level, and that was a really good performance, but we just couldn't get the win."
There could also be further ramifications from the match for Celtic after fans defied a club plea by waving Palestine flags in a show of support to people in Gaza during the war between Israel and Palestinian militants Hamas.
A leading Celtic fans' group announced they would distribute flags outside the stadium.
In a statement before the match, Celtic asked that "banners, flags and symbols relating to the conflict and those countries involved in it are not displayed at Celtic Park at this time".
Celtic have twice been fined by UEFA in the past for the flying of Palestinian flags.
- Celtic inspired -
Once the action got underway, the home side were inspired by the hostile atmosphere.
Matt O'Riley's through ball sliced open the Atletico defence for Kyogo to dink home his seventh goal of the season.
But Celtic have found the step up to Champions League level tougher defensively and a naive challenge from Greg Taylor on Nahuel Molina handed the visitors a glorious chance to equalise.
Joe Hart tipped Griezmann's spot-kick onto the woodwork, but the ball bounced back kindly for the French international to roll into an empty net.
Celtic hit back within three minutes when Palma blasted into the far corner from Daizen Maeda's cross.
Atletico thought they had levelled again before half-time only for Axel Witsel's header to be ruled out for offside.
Diego Simeone's men did not have to wait long after the break to equalise when Morata stooped to divert a brilliant header high past Hart from Marcos Llorente's cross on 53 minutes.
Atletico then looked set to go on and win the game as Celtic paid for their first-half efforts by tiring in the second period.
But De Paul dived in on Paulo Bernardo to earn a second yellow card and at least give the hosts some breathing space in the closing stages, even if they failed to find a winner.
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