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

A second-half hat trick by substitute Moussa Dembele secured what was ultimately a comfortable 5-2 victory for Brendan Rodgers’ side, as they recorded a 19th consecutive victory.

The Frenchman’s goals helped to ensure the champions moved 27 points clear of Aberdeen at the top of the Ladbrokes Premiership and remain on course to win the league 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 referee Thomson awarded Celtic a dubious spot-kick when they were trailing their hosts by a goal.

Liam Henderson had given the visitors the lead after only six minutes when he drilled a low shot beyond Zander Clark from 15 yards out. The Parkhead side should then have added to their tally, but Gary Mackay-Steven – who was given his first start for Celtic in six weeks – passed up two excellent chances to score as the visitors dominated the opening exchanges.

Tommy Wright’s St Johnstone side fought their way back into the game and Craig Gordon did well to deny Richard Foster after a defence-splitting pass by Danny Swanson after 18 minutes.

But Keith Watson levelled for the home side in the 31st minute after rising unopposed inside the penalty area to meet a Swanson corner and head the ball powerfully beyond the goalkeeper. It was the former Dundee United, Hibernian and St Mirren right-back’s first goal for the club he joined in the summer.

Another curling Swanson delivery into the Celtic box just two minutes before half-time allowed St Johnstone to snatch a lead. David Wotherspoon sent a header towards goal and the ball deflected off Dedryck Boyata on its way into the net.

St Johnstone then had a strong claim for a penalty waved away by Thomson after the break, when Swanson appeared to be barged over in the box by Celtic captain Scott Brown. The home side’s feeling of injustice at that decision only increased after 61 minutes when Thomson ruled that Watson had handled a Kieran Tierney cross inside the 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, drilling a shot beyond the outstretched Clark and into the top left corner of the net.

Dembele registered his 22nd goal of the campaign after getting on the end of a Mikael Lustig cut back, steering the ball beyond Clark.

Scott Sinclair added another goal after receiving a pass from Patrick Roberts, before 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 Rodgers’ side have now moved 27 points ahead of Aberdeen at the top of the Premiership and remain on course to win the title in record time.

The Celtic support was still celebrating that fact as Liam Craig and Lustig were booked after squaring up to each other at the end.