In between the first two goals, defender Jozo Simunovic was shown a straight red card by referee Haratiu Fesnic for a high challenge on Jefferson Reis.

But the home side remained dominant until the final whistle to go through 6-0 on aggregate and set up a meeting with Rosenborg in the next round, with the first game taking place at Celtic Park next week.

Celtic's convincing first-leg win had taken the tension out of the return game, but with season tickets valid there was a good crowd inside the stadium for the first competitive home game of the season.

Brendan Rodgers started the same side which began in Armenia and unsurprisingly they took control of the early stages, taking the lead in the seventh minute due the tenacity of Dembele.

He refused to buckle under a couple of tackles inside the box before finding the corner of the net with a shot from 12 yards.

There was some anger among the Parkhead fans, however, four minutes later, when a tackle on Reis by Simunovic close to the halfway line was deemed to warrant a red card by Romanian official Fesnic.

Jack Hendry moved from right back into the centre of defence with James Forrest covering but there was little difference to the flow of the game.

In the 18th minute Celtic were awarded what looked like a soft penalty when midfielder Artak Grigoryan tackled Odsonne Edouard in the penalty area but when the fuss died down Dembele confidently slotted home the penalty.

The game ambled along with the Glasgow side still in control, albeit the fact goalkeeper Craig Gordon did well to push away a powerful drive from skipper Artak Grigoryan for a corner which came to nothing.

Last season's treble winners showed their clinical side again following a swift break in the 35th minute when Edouard played in Forrest, who drilled the ball low past Alashkert keeper Ognjen Cancarevic from 16 yards.

The threat of more goals remained strong and Cancarevic made a fine fingertip save on Kieran Tierney's long-range drive moments after the restart.

The tempo of the game then dropped a couple of notches as Celtic legs tired, but no more than their ragged opponents.

Scott Sinclair replaced Edouard in the 64th minute, with Ryan Christie coming on for Dembele a minute later to change the make-up of the Celtic attack and inject some urgency.

Cancarevic made saves from Forrest and Callum McGregor and then, in the 74th minute, Sinclair sent Christie clear but he smashed his shot straight at the overworked Alashkert keeper.

Teenage winger Mikey Johnston, linked with both Hibernian and St Mirren, replaced Forrest moments later and he helped Celtic see the game out and ease into the next round.