Mark Viduka again emerged as Celtic's saviour to rescue a match against St Johnstone which was drifting away for the Parkhead outfit in a season in danger of doing the same.

Next week's CIS Cup final with Aberdeen now represents Celtic's most realistic hope of silverware this term given Rangers' commanding lead at the top of the Scottish Premier League.

But after claiming his 26th and 27th goals of a prolific campaign it is difficult to see a stronger contender than Viduka for Scotland's Player of the Year.

It was his junior striking partner Mark Burchill who put Celtic ahead after 18 minutes, but Paddy Connolly levelled matters before the interval to leave the home side reeling.

Still shaken by Wednesday's vital 1-0 home loss to title rivals Rangers, Celtic needed inspiration midway through the second half and, as so often this year, Viduka provided it.

A double strike, the first a header on 64 minutes, the second - just five minutes later - a clinical strike to complete a move he started himself enlivened a sluggish display.

For long periods this match resembled an end-of-season contest, the bright sunshine only adding to the illusion, but when Burchill made it 4-1 after 71 minutes at least the mood had been lifted.

Now Kenny Dalglish's Celtic must hope they can repeat the energy and poise of that second-half scoring burst at Hampden Park next Sunday to take something from a troubled season.

Injuries to Johan Mjallby and Alan Stubbs meant Brazilian international Rafael made his first Celtic start since his £4.8million switch from Gremio despite lacking match fitness.

With Lubomir Moravcik rested after his midweek exertions, Eyal Berkovic made a rare start and his threaded pass almost put Mark Viduka through only for youngster Stephen Robertson to pass his first test by moving smartly from his goal.

Robertson is third choice at McDiarmid Park but Alan Main's groin operation and Allan Ferguson's severe knee injury means he has been given his chance.

Burchill came close to opening the scoring on 16 minutes when he cut inside after being fed by a clever Berkovic flick, but his snap shot was sent into the side-netting.

A mere two minutes later however and the Scotland international made no mistake netting with a low volley when picked out unmarked at the far post by Viduka's searching deep cross.

At 1-0 down Saints' limited gameplan looked in danger of collapsing around them, Robertson needing to clutch a fierce angled drive from Viduka at the second attempt.

Celtic were showing signs of relaxing and their play started to show some much-needed fluency, Morten Wieghorst's quickly-taken free kick setting up Berkovic for a 20-yard shot well saved.

Yet Celtic's makeshift defence were found wanting in Saints' first attack of note, Stephen Frail's cross headed down by Keith O'Halloran for Connolly to beat Jonathan Gould to the ball.

The keeper looked slow to react to the danger and Connolly, re-established as first choice striker for Saints after a long battle with injury, seized his opportunity to level the scores.

Viduka was clean through after 36 minutes but, as in midweek, his usually reliable finishing was absent as he flicked a shot wide of the mark when clean through on Robertson.

Rafael was replaced at the break by Olivier Tebily while St Johnstone took off Weir and brought on Kieran McAnespie - both changes presumably prompted by fitness reasons.

By the hour mark, Celtic were looking badly short of ideas, a woeful shot wide from distance by Stilian Petrov summing up their lack of invention, likewise a wayward Mahe effort.

However on 64 minutes, Berkovic delivered a superb free-kick for Viduka to rise above the Saints defence and nod past Robertson for 2-1.

It was a goal which brought the contest back to life, Mahe playing in Viduka again moment later for a well-struck shot just wide as Celtic finally clicked into gear.

After 69 minutes, the match was effectively won when Celtic moved 3-1 ahead after more impressive play from Viduka who started and finished a goal out of virtually nothing.

Beating Dods in the air to hold up the ball, Viduka's immense strength won the time to introduce Berkovic to the play and the Israeli returned the pass for the Australian to fire home.

There was a sour note for Celtic after 70 minutes when Mahe was needlessly booked for an off-the-ball altercation with Frail and when play resumed he was substituted for Regi Blinker.

Celtic next act was to stretch their lead still further, Viduka finding Burchill's run and the youngster slotting confidently beyond Robertson for an emphatic 4-1.

Saints still had more to offer, substitute Nathan Lowndes hitting the side-netting, then a Gary Bollan free-kick troubling a nervy-looking Gould, but their cause was lost.

Lowndes missed badly with 10 minutes remaining when he should have picked out John O'Neil's run, but still it was Celtic who were holding the real threat.

Viduka was only denied a deserved hat-trick by an astonishing save from Robertson in the 87th minute, but attention was already shifting to what might happen next Sunday.

Teams

Celtic: Gould, Riseth, Boyd, Rafael (Tebily 46),McNamara (Creaney 77), Petrov, Wieghorst, Berkovic,Mahe (Blinker 70), Viduka, Burchill.

Subs Not Used: Kerr, Healy.

Booked: Mahe.

Goals: Burchill 17, Viduka 65, 68, Burchill 70.

St Johnstone: Robertson, Dods, Weir (McAnespie 46), Griffin,Bollan, Frail, O'Halloran, O'Neil, Kane, Connolly (Lowndes 65), McBride.

Subs Not Used: Cuthbert, McMahon, Jones.

Booked: O'Halloran, Frail.

Goals: Connolly 34.

Att: 59,530

Ref: John Rowbotham (Scotland).