Celtic manager Neil Lennon praised the workrate of his players, in a vital Europa League Group I match.
Arda Turan's solitary strike after 30 minutes separated the sides, but Lennon insisted his players were equal to the Spanish visitors.
"I thought we matched Atletico for the majority of the game - if not bettered them," said Lennon.
"It was an excellent performance, and I thought we deserved better from it."
Gary Hooper had a goal ruled out for Celtic during the second half in Glasgow, with Anthony Stokes adjudged to have handled it along the way.
And Ki Sung-Yeung's free-kick in the 67th minute was deflected over by Atletico keeper Thibaut Courtois, denying Celtic a leveller.
The Spanish visitors held out for the three points and progress to the latter stages of the tournament, while Celtic need a win from their last group match away to Udinese to remain in the competition.
"It's a tall order - Udinese are an excellent side," said Lennon.
"We haven't won away from home in a long while, but we'll give it everything we've got.
"I'm delighted with the way the players played tonight, and I couldn't recriminate any of them - they had a good go, and they're a good side.
Celtic captain Beram Kayal appeared at fault when the deadlock was broken in the 30th minute: standing on the six-yard line, he ducked to avoid Turan's strike and it sailed past Forster into the back of the net.
However, Lennon refused to blame the Israeli midfielder for the goal and insisted that the defeat will give Celtic more impetus to win their final match.
"He misjudged the flight of the ball and Fraser didn't see it until late, so he couldn't really do much about it," said Lennon.
"He did his best, which was a split-second reaction.
"I'm not going to be over-critical of the goal - they defended the corner well. It just got through a ruck of bodies and he didn't see it until late.
"Up until that, it was the only difference between the sides. We created more chances tonight than we did against Rennes and we didn't win the game.
"We played well against a top quality side, and, if anything, I think it'll give us more determination.
"There were some brilliant performances out there tonight - [Georgios] Samaras and Kayal didn't look out of place - I thought they were among the best players on the pitch.
"But for a bit of luck, we would have won the game."