Henrik Larsson headed his 44th goal of the season to move Celtic 16 points clear at the top of the Scottish Premier League and within touching distance of the championship.

But a late injury to Stilian Petrov soured an otherwise perfect evening when he was stretchered off late on with a suspected broken ankle.

While Larsson grabbed the headlines with his second-half winner, his strike-partner Tommy Johnson staked his claim for a place in Sunday's League Cup final.

Johnson looked lively during the first half and almost bagged the opener in the 24th minute, timing his run perfectly to beat the off-side trap and collect Larsson's pass, but he fired low from a tight angle and Main saved.

But Johnson was celebrating four minutes later when he broke the deadlock after Thompson swung over a corner and the unmarked striker headed home from just six yards.

St Johnstone, however, hauled themselves back on level terms in the 42nd minute when Neil Lennon was adjudged to have brought Momo Sylla down just wide of the box after he had left a number of Celtic players in his wake.

Paul Kane curled in a dangerous free-kick and McCluskey found space to head past Douglas into the corner of the net.

But Celtic were not to be denied and when midfielder Thompson curled in a free-kick from the right flank, Larsson out-jumped the St Johnstone defence to head the ball into the corner.

St Johnstone: Main, Weir, Kernaghan, McCluskey, Frail (Hartley 78), Forsyth, Dasovic, Kane, Crozier (Lovenkrands 67), Sylla, Parker. Subs not used: Cuthbert, O'Neill, McClune. Booked: Kernaghan. Goal: McCluskey 41.

Celtic: Douglas, Valgaeren, Mjallby, Vega, Thompson, Agathe (Crainey 90), Lennon, Lambert, Petrov (McNamara 83), Johnson, Larsson. Subs not used: Gould, Boyd, Moravcik. Goals: Johnson 28, Larsson 61.

Referee: J Underhill (Scotland).