Champions-elect Celtic kept their Double dream alive at Hampden Park as they saw off plucky Ayr.

Martin O'Neill's had their bid for back-to-back clean sweeps snatched from their grasp by Rangers at Hampden Park.

But a Henrik Larsson goal and Alan Thompson brace erased that memory with a second-half winner to put Celtic into the final of the Tennent's Scottish Cup - against Rangers or Partick.

The national stadium proved to be an unhappy hunting ground for the First Division side, who gave Celtic - and Rangers last week - plenty to worry about before leaving empty handed.

But Ayr left with plenty to be proud of in the knowledge they had given the Parkhead outfit a major scare on the way and created more chances than most Premier League sides have mustered against them all season.

The big sections of empty seats and the amazing low-key atmosphere certainly made a mockery of the Scottish Football Association's decision to stage the semi-final at Hampden Park.

But nothing was going to spoil Ayr's second big day in Glasgow - not even another heartbreaking defeat and late flurry of goals.

Celtic though seemed to find it difficult to rise to the occasion as the First Division side made the brighter side as they did in last week's CIS Insurance Cup final against Rangers.

In fact, Celtic goalkeeper Robert Douglas needed to make a good save in the 15th minute to prevent Ayr taking a shock lead.

Pat McGinlay played the ball in field to John Robertson and the full-back hit a rasping left-foot shot which Douglas needed to save at full stretch low to his right.

But like Rangers before them, the Glasgow giants eventually came to life in the 23rd minute when they threatened the Ayr goal.

John Hartson nipped the ball away from skipper John Hughes and fired a right-foot shot just past the upright.

Celtic again sliced the Ayr defence open eight minutes later following a neat interchange of passes between Larsson and Hartson, but the Welshman again pulled his shot wide of the post.

But O'Neill was forced to make a change in the 29th minute after Steve Guppy's studs appeared to get caught in the turf and he was replaced by Alan Thompson.

The winger pointed at the pitch as he passed O'Neill, who is has already heavily criticised the state of the Hampden Park pitch.

But that failed to stop Celtic's momentum and on the half-hour Hughes prevented the champions-elect from scoring the opener.

Hartson did well down the right and crossed, but the veteran managed to get a head on the ball to take it away from Larsson.

But the underdogs missed a glorious chance to take the lead just three minutes before the break.

Bobo Balde failed to deal with Craig Nelson's long punt downfield and James Grady nipped in to poke the ball past Douglas, but unfortunately for him also passed the Celtic post.

The Hoops breathed another sigh of relief a minute later when space opened up for Paul Sheerin to try a shot and Douglas could only push away his powerful left-foot strike.

O'Neill would have given his side a rollicking in the dressing room and they stepped up a gear immediately after the restart.

Larsson squandered a great opportunity to settle his side's nerves in the 47th minute after Thompson had picked him out in the box, but the Swede headed just wide from eight yards out.

The striker, however, made no mistake in the 49th minute when he poached to give Celtic the lead.

Agathe's quick burst of pace left Paul Lovering in his wake and Larsson got away from Hughes to prod the Frenchman's cross home between Nelson and his left-hand post from close range.

But the Somerset Park side refused to let their heads down and came back with a great chance in the 63rd minute.

McGinlay found the overlapping Lovering, who crossed to the far post, but Robertson outclimbed Lennon and headed just over.

Ayr came even closer to an equaliser in the 69th minute when Balde again failed to clear substitute Eddie Annand's cross and Grady's fierce left-foot drive came back off the crossbar.

Larsson tried to kill off Gordon Dalziel's courageous men a minute later, but he dragged his right-foot wide.

Ayr still came at Celtic and again Douglas maintained his side's one-goal lead in the 77th minute.

Annand knocked down Hughes' long ball downfield and Grady caught it full on the volley, but the keeper pulled off a fine stop to his left.

Celtic star Thompson though eased his side's nerves in the 81st minute with a spectacular strike.

Sheerin fouled Agathe and the midfielder struck a glorious left-foot free-kick from 25 yards past the despairing dive of Nelson and into the top corner.

Thompson curled his second with three minutes remaining after Hartson had squandered a good chance which was cruel for Ayr.

They deserved the after-match applause - while Celtic will be looking to finish off the season in style with the Premier League and Scottish Cup trophy in the Parkhead cabinet.

Teams:

Celtic: Douglas, Mjallby, Balde, Crainey, Agathe, Lambert, Petrov (McNamara 84), Lennon, Guppy (Thompson 29), Hartson, Larsson.

Subs Not Used: Gould, Boyd, Moravcik.

Booked: Thompson.

Goals: Larsson 49, Thompson 81, 88.

Ayr: Nelson, Robertson, Hughes, Duffy, Craig, Lovering, McGinlay, Wilson (McLaughlin 83), Sheerin, Crabbe (Annand 67), Grady.

Subs Not Used: Dodds, McEwan, Sharp.

Booked: Wilson.

Att: 26,774

Ref: S Dougal (Scotland).