ST. JOHNSTONE'S players were left incensed after a hugely controversial penalty decision by referee Craig Thomson allowed Celtic to level in a match they had been trailing 2-1 in.

A second-half hat-trick by substitute Moussa Dembele secured what was ultimately a comfortable 5-2 victory for Brendan Rodgers's side.

The Frenchman's goals helped to ensure the Glasgow club moved 27 points clear of Aberdeen at the top of the Ladbrokes Premiership and on course to win the Scottish title in record time.

The emphatic result also extended Celtic's record-breaking unbeaten run domestically to 29 games.

But this latest win was only achieved after Thomson had awarded Celtic a dubious spot kick when they were trailing 2-1 after an hour.

Liam Henderson had given the visitors the lead in just the sixth minute when he drilled a low shot beyond Zander Clark from 15 yards out.

The Parkhead club should have added to their tally during early exchanges which they dominated, but Gary Mackay-Steven, handed his first start in six weeks, passed up two scoring chances.

Tommy Wright’s charges fought their way back into the game and Craig Gordon did well to deny Richard Foster after a defence-splitting pass by Danny Swanson in the 18th minute.

But Keith Watson levelled for St. Johnstone in the 31st minute after rising unopposed to meet a Swanson corner in the Celtic area and heading beyond the keeper.

It was the former Dundee United, Hibernian and St. Mirren right-back’s first goal for the club he joined back in the summer.

Another curling Swanson delivery into the Celtic box just two minutes before half-time was headed into his own net by Dedryck Boyata.

St. Johnstone had a strong claim for a penalty saved away by Thomson in the 50th minute after Swanson appeared to be barged over by Celtic captain Scott Brown.

The Saints players’ unhappiness at that decision increased in the 61st minute when Thomson ruled that Watson had handled a Kieran Tierney cross inside his own area.

The match official was surrounded by blue shirts, but their appeals were waved away and Dembele, who had just replaced Mackay-Steven, stepped up to take the spot kick.

The Frenchman made no mistake – he drilled his attempt beyond the outstretched Clark and into the top left corner.

Dembele bagged his 22nd goal of the 2016/17 campaign in the 75th minute after getting on the end of a Mikael Lustig cut back and slotting a right foot shot into the net.

Scott Sinclair added another six minutes after receiving the ball from Patrick Roberts and Dembele completed his hat-trick when he rounded off a delightful move with five minutes remaining.

It was the first time the 20-year-old had scored three goals since Celtic’s 5-1 win over Rangers at Parkhead in September.

Brendan Rodger’s side moved 27 points ahead of Aberdeen at the top of the Premiership as a result of the 5-2 and remain on course to win the title in record time.

Both Liam Craig and Lustig were booked as players squared up to each other after the final whistle.