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Substitute Moussa Dembele scored a hat-trick as Celtic came from behind to beat St Johnstone and go 27 points clear at the top of the Premiership.

Liam Henderson's goal for the visitors was cancelled out by Keith Watson's header and David Wotherspoon's effort went in off Celtic's Dedryck Boyata.

Dembele converted a controversial penalty to equalise and then fired the visitors ahead.

And further strikes by Scott Sinclair and Dembele followed.

Brendan Rodgers remains unbeaten by domestic opponents as Celtic manager and his side have now won 19 league games in a row.

St Johnstone trail fourth-placed Hearts by three points but remain 10 ahead of Motherwell.

Wright critical of ref against Celtic

Sizzling start

St Johnstone boss Tommy Wright was determined to snuff out the danger posed by Celtic youngster Kieran Tierney and so pushed Richard Foster into the midfield to keep him company but it was another Celtic youngster who helped the champions draw first blood.

Liam Hendreson, Patrick Roberts and Gary Mackay-Steven all started with real drive and intent for the visitors and after Zander Clark pulled off two good saves from Roberts and Mackay-Steven, Henderson curled the ball beautifully past the Saints number one.

Henderson (far right) scored his first Celtic goal in over two years

It was just reward for a sizzling start and at that stage the home side were struggling to deal with Celtic's energy in midfield.

But this St Johnstone side, the last to beat the champions way back at the end of last season, rarely buckles and that is down to belief.

Saints fight back

As expected, Celtic were enjoying most of the possession, but after the goal they were wasteful with their chances and the home side started to venture out with the odd probing counter attack and were rewarded from a set play.

Danny Swanson curled in a sumptuous corner from the right and Watson's sheer will took him above the Celtic defence where he bulleted a header past goalkeeper Craig Gordon, with the ball taking a nick of Celtic captain Scott Brown's head.

The champions were rocked but there was worse to come for them before the break as Saints sensed some rare vulnerability.

Again Swanson was the man who provided the inch-perfect cross, this time from the left on the counter attack. His ball found the head of Wotherspoon inside the box and he deftly flicked it backwards where it bounced off Boyata and into the net.

Boyata had scored the winner in Celtic's last game against St Johnstone

They got the breaks they needed but it was no more than their efforts deserved in the first half.

Spot-kick controversy

Fearing for their unbeaten run, Celtic came out in the second half determined to turn the screw and poured forward in waves. Saints were holding them at bay, though, until a penalty award that infuriated Wright and his St Johnstone players.

Tierney left Foster on the floor with some trickery at the edge of the box but his cross was cut out at close range by Watson, who twisted his body away as he fell, and referee Craig Thompson immediately pointed to the spot for handball.

It looked harsh but despite the protests, Dembele, just on for Mackay-Steven, stepped up and blasted high past Clark to level.

Dembele came on after missing Celtic's last two games

Celtic class

The home side knew they now had a mountain to climb as Celtic sensed the tide turning - and turn it most certainly did.

Top scorer Dembele's low drive from 16 yards after fabulous build-up play put them ahead before Sinclair made it four after good running from Roberts.

With the game won it was showboating time and the fifth was simply sublime.

Mikael Lustig's rabona inside the box found sub Callum McGregor, who had a flick of his own into the path of Dembele and the Frenchman smashed in his hat-trick and 23rd goal of the season.

It was hard to take for the St Johnstone fans who thought for a time that the seemingly impossible might just be possible but it was a thing of beauty to seal Celtic's 29th unbeaten domestic game since the start of the season.