Celtic went into the confrontation with the knowledge nearest rivals Aberdeen had shed two points in their 1-1 draw with Dundee at Dens Park in the 12.15pm kick-off.
Mackay-Steven opened the scoring and did most of the damage. He was ineligible for the Cup-ties, along with team-mate Stuart Armstrong, but he wasted no time in marking his return with a sweet strike from 20 yards to break the deadlock in the 16th minute.
He latched onto a pass from Efe Ambrose and anbled forward before unleashing a screaming shot from outside the box. Goalkeeper Radoslaw Ciernzniak was well beaten as the effort swept past him at his right hand side.
In the 33rd minute, GMS exchanged passes with John Guidetti before the Swede crashed a deflected shot from the edge of the box high into the net. After that two-goal salvo, United were on their knees and it was a canter for the champions.
Guidetti’s complete lack of celebrations hardly endears him to the Celtic support. If he’d rather be elsewhere he should just say so. It’s a privilege to wear the Hoops John, so please don’t abuse it.
After six red cards in the previous outings, this was a reasonably tame affair, but Paul Paton still managed to get himself booked just on half-time with a stupid swipe at former team-mate GMS.
Referee Kevin Clancy produced a yellow card, but Stefan Johansen wasn’t finished with the retribution and rolled the free-kick across the box to Virgil van Dijk.
The Dutchman’s shot was charged down, but Jason Denayer was alert in the six-yard box and took a touch before back-heeling into the net to put the tin lid on a miserable 45 minutes for the Tangerines.
Understandably, Deila’s team took their foot from the pedal after the restart with the game won.
Keeper Craig Gordon was called upon to make a couple of saves from sub Ryan Dow and defender Paul Dixon, but Celtic could also have added to their tally as they sauntered through to full-time without fuss to take another big step towards more glory.
Deila’s men are now 12 games away from the treble. In this sort of form, you wouldn’t bet against them. Dundee United’s season is over and Jackie McNamara will now be “under pressure” to try to get some wins out of his very average group of players as he attempts to save his job.
TEAM: Gordon; Ambrose, Denayer, Van Dijk, Izaguirre; Bitton, Brown; Mackay-Steven (sub: Commons 70), Johansen, Armstrong (sub: Henderson 76); Guidetti (sub: Scepovic 70).