The Hoops were brought back down to earth after their brilliant 2-1 home victory over Barcelona a fortnight ago and now need to beat Spartak Moscow and hope Barce get the better of Benfica in the final group stage game if they are to progress.
Smaras, who netted Celtic's goal in the 32nd minute, admitted Neil Lennon's side played with nerves in Portugal but is confident they can bounce back against Spartak at Parkhead on December 5.
"For the full 90 minutes we were a little bit nervous," said Samaras. "We didn't have a clear mind but it's finished.
"I didn't think we played really well but the game was really close. The only thing we can keep is the team effort and the really hard work we had.
"We are just looking forward to the next game and we must stay positive.
"We still have a chance to go through and we will do our best to go through to the next round."