It’s not all glamour.

On the night when Celtic posted considerable pre-tax profits thanks to their Champions League involvement last season, there was a reminder in the steady rainfall at a creaking Dens Park that it’s the basics which lay the foundations for the bigger picture.

Scott Sinclair started the ball rolling while a double from James Forrest and another one for Callum McGregor gave Celtic a ticket into the semi-finals of the Betfred League Cup without ever breaking sweat.

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There was a certain mundanity in the return to League Cup action but it is to Celtic’s credit that their focus does not appear to be punctured when the prestige can be a little wanting.

There were six changes made to the team that hammered Ross County at the weekend with the return of Dedryck Boyata the notable addition following a three-month injury lay-off, while Jozo Simunovic’s absence with a swollen knee raised questions of their own.

Moussa Dembele was, as expected, rested after playing an hour at the weekend with Rodgers keen to nurse the striker back to full fitness after two successive hamstring injuries.

The disruptions to personnel, however, did not detract from Celtic’s fluency.

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By the time this game was at its half-way stage, the Parkhead side would have been booking the bus for another trip to the national stadium.

The procession towards the semi-final of the League Cup began in earnest midway through the opening half.

It was Sinclair, relatively quiet until then, who brought the game to life with a run full of pace and menace and aggression that took him into the Dundee box where he was upended by Jack Hendry.

It was an unambiguous penalty call, with Sinclair stepping up to convert the set-piece himself. Dundee keeper Scott Bain guessed correctly as he dived to his left but the ball had too much power for him to repel it.

There had been a physical opening to the game with Kieran Tierney taking a hefty kick from Randy Wolters and Hendry decking Olivier Ntcham in the early stages.

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Celtic, though, on a surface saturated by torrential rain the build-up to the encounter, weathered the onslaught and in truth came out of the game without being genuinally questioned.

In saying that, with the score still at just 1-0. Faissal El Bakhtaoui had a glorious chance to level proceedings. A whipped cross from the left foot of Wolters looked set to drop invitingly for the striker but he took his eye off the ball and walloped fresh air with Craig Gordon at his mercy.

If he had cause to lament the chance that passed him by, its costliness was brought into sharp focus shortly after when Celtic doubled their advantage and effectively put the tie beyond the reach of their hosts.

Tierney and James Forrest combined for Celtic’s second, with the former sliding the ball into the penalty box where the latter slid down to connect and guide into the far corner.

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It was Forrest’s sixth of the season - he would go onto add his seventh - a number that grows in significance when consideration is afforded to the fact his best return for Celtic over the course of a campaign is nine.

All things being well the expectation is that Forrest could well go on to enjoy his best season yet at Celtic, an interesting thought given the number of options that Brendan Rodgers has at his disposal for wide men.

The second period started in the same vein that the first had ended with Leigh Griffiths forcing a corner after a long-range effort was deflected for a corner. The move came to nothing but it was a reminder for Dundee that they were in for a long evening.

There was frustration on the part of Dundee with Patrick Roberts feeling the sharp end of it. The winger was sent crudely air-borne by a lunge from El Bakhtaoui which earned the forward a booking while Tierney spent more of his night on the turf than he did on his feet given the regularity with which he was chopped on the flank, Cammy Kerr joined the list of miscreants in the book following one particular chop on the Scotland internationalist.

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Forrest smashed an effort off of Bain as Celtic looked for more, but it was the movement of Sinclair and Tierney on the left-hand side that was the real problem for Dundee.

It was persistently from that flank that Celtic's chances came, with Dundee toiling to cope with the pace and trickery of the duo.

Anthony Ralston, a substitute for Roberts, felt the boot of Darren O'Dea, giving Griffiths a chance to impress with a free-kick.

The striker will have to wait, though, to repeat his June heroics as he ballooned the effort high and wide.

Inevitably, though, a third and then a fourth came.

It was substitute McGregor who set the seal on the evening when he netted a rasping, low finish into the bottom corner.

Within a minute, there was another when Forrest added his second.

As defences go, Celtic's protection of their winners' status of this tournament was resolute.