The runaway Primera Liga leaders booked their place in the last 16 of the competition with AC Milan but they were punished for failing to kill off Martin O’Neill’s gutsy side, who went some way to healing the wounds of Saturday’s shameful Old Firm defeat.

Barcelona were flying after their 3-0 victory over Real Madrid at the weekend and they were expected to run up another emphatic win after Samuel Eto’o’s opener.

But through bad finishing they paid the price with John Hartson enhancing his chances of a new contract by giving Martin O’Neill something to smile on the stroke of half-time.

The surprise draw revived their hopes of staying in Europe beyond Christmas as it took them a point above Shakhtar Donetsk in Group F with just one game remaining.

It was also Celtic’s first away point in the Champions League under O’Neill.

The Northern Irishman made just one change to his starting XI following the ugly Old Firm scenes with Didier Agathe coming in for Henri Camara but Barcelona were expected to coast to victory.

Neil Lennon had to be spoken to by referee Lubos Michel for a clash with Deco before he unnecessarily went into the book in the 10th minute for dissent.

O’Neill also had to be calmed down by the fourth official on the sidelines as he protested against a decision.

The home side gave Celtic a warning in the 24th minute when Juliano Belletti pulled the ball back for Ludovic Giuly but his shot was saved by Magnus Hedman.

But Celtic failed to learn from that and they were sliced wide open less than a minute later as Barcelona took the lead.

Eto’o exchanged passes with Deco to leave the Hoops defenders bemused and he coolly fired low past the Swedish goalkeeper.

The Cameroon striker should have put the game out of Celtic’s reach moments later after Sylvinho had picked him out in the area but he pulled his effort just wide.

Hedman looked unconvincing from the start and he was anxiously scurrying back to his goalline in the 32nd minute as Deco’s shot spun up into the air off Stanislav Varga.

The Celtic defence were in tatters again moments later as Eto’o played another superb one-two, this time with Giuly, but the visitors somehow managed to survive.

They were hanging on again in the 36th minute as Hedman stopped Giuly’s point-blank effort and then Ronaldinho put the ball over with the goal at his mercy.

Rafael Marquez joined Lennon in the book for a crude foul on Varga before Hedman came to Celtic’s rescue to keep them in the game.

Ronaldinho cut the ball back to Eto’o, who steadied himself and blasted the ball low, but the Swede kept the ball out with his leg.

But Celtic snatched the equaliser on the stroke of half-time to stun the passionate Nou Camp crowd as Barcelona slept.

Sutton won a free-kick and then dummied Stilian Petrov’s set-piece and Hartson arrived at the back post to poke the ball over the line.

Frank Rijkaard’s team seemed stunned in the early part of the second half and the Dutchman tried to effect a change by bringing on Andres Iniesta for Giuly after an hour’s play.

The Swede comfortably saved Ronaldinho’s low free-kick in the 63rd minute after Bobo Balde fouled Deco.

The visitors breathed a sigh of relief in the 77th minute when Xavi’s effort took a wicked deflection off Petrov and spun inches past the upright with Hedman rooted to the spot.

Celtic have a nasty habit of conceding late goals in the Champions League, which cost them in Milan, but they defended resolutely.

O’Neill made another change with four minutes left to go on the clock with Ross Wallace coming on for a weary Thompson, who had forgotten his sending-off on Saturday.

Barcelona pressed right to the final whistle but the Hoops held on and can now hope for a place in the UEFA Cup if things go their way in the final group matches.