A HISTORIC successive treble remains on for Celtic even if they made heavy work of their victory over Morton.

A second-half double by Moussa Dembele was the biggest aspect in what in the end it was a simple enough passage to the Scottish Cup semi-final.

Celtic, however, were sluggish again in front of a sparse crowd on a freezing cold day in Glasgow’s east end.

The weather meant Morton had not been able to prepare to properly for this game, and their manager Jim Duffy must have been delighted with his players.

The game went something like this.

Morton allowed Celtic to have lots of the ball and when not in possession, got everyone back to form a defensive line which reduce the home side to speculative long-range shots for much of the tie.

And when the Championship side attacked, they did so with intent; however, the difference in class told in the end.

Celtic aren't playing at their best but they keep winning.

Marvin Compper, signed in January, got his long-awaited start for Celtic and the German’s touch gave away possession and corner to Morton. It could only get better.

Celtic’s first chance came after 15 minutes. Dembele and James Forrest swapped passes inside the box, the winger crossed back in for the striker whose header was going in until Tom O’Ware made a crucial block on the line.

Kristoffer Ajer put a header wide on 37 minutes and then, moments later and following a flowing Celtic move, Morton keeper Derek Gaston pulled off a superb save to deny Tom Rogic a goal.

Rogic went close again on 41 minutes, this time his volley was pushed behind by Gaston.

It was a dour half of football, certainly as far as Celtic were concerned, and Rodgers reacted at the break by replacing Scott Sinclair, again worryingly ineffective, and Odsonne Edouard came on.

The second half was a lot better and the substitute should have opened the scoring with his first touch.

Celtic passed their way into Morton’s box, the ball fell kindly to Edouard but his shot was far too soft and Gaston’s task of making a save was far simpler than it should have been.

Morton came to close to scoring a goal themselves on 54 minutes.

Following some decent passion by the Greenock outfit deep in Celtic’s half, left-back Andrew Murdoch played a bit of keepie-uppie at the edge of the box, got a shot off which whizzed past the post.

Gaston made a fine stop on the hour when he kept out Olivier Ntcham’s fiercely hit drove from distance.

And the dreadlock was eventually broken by Celtic two minutes later.

Rogic was one of the few enjoying a productive afternoon and therefore it was little surprise that he was involved; the Australian’s cross was met by Dembele whose header sent the ball home via the underside of Galston’s crossbar.

The game was all over on 70 minutes.

Referee John Beaton pointed to the spot when Dembele’s mazy run was crudely ended by Morton defender Michael Doyle who argued that contact had taken place outside his box. The Frenchman took the penalty himself and gave Galston no chance.

Dembele was denied a hat-trick late on, this time the excellent Galston got a hand to the striker’s well aimed header, and the Morton keeper also got behind a Ntcham half volley.

However, a third goal was scored at the death; Forrest showed good skill on the right to get the ball to Edouard's feet, the teenager took a nice touch before shooting high into the goal.

Celtic v Morton in pictures