Celtic completed a blockbuster Scottish Cup semi-final line-up with a hard-earned victory over Dundee United.
Ange Postecoglou 's side will join Rangers, Hearts and Hibs in the final four at Hampden thanks to Callum McGregor and a double from the returning Giorgos Giakoumakis.
The Parkhead side were shorn of Jota and Liel Abada for an ever-perilous trip to Tannadice but again showcased their increased strength in depth with a clinical display.
McGregor's deflected effort secured a crucial early advantage before Giakoumakis pounced on an error from keeper Benjamin Siegrist to thwart United's rising resistance in the second period.
Celtic remain in the hunt for a Treble and are now unbeaten in their last 30 domestic matches, a run which stretches all the way back to September.
They were met by United's characteristic commitment and discipline but were rarely troubled Tam Courts' team.
Giakoumakis replaced the injured Jota and James Forrest kept his place in Abada's absence, with Daizen Maeda moving to the left hand side.
Maeda had a sizeable away support off their seats in the opening moments as his ambitious lobbed effort landed on the roof of Siegrist's net.
The first sign of life from the home end was sparked by an early penalty claim that never was when Marc McNulty went down under pressure from Carl Starfelt but, if anything, it was the United striker who had grip of the Swede's shirt and John Beaton was uninterested.
Minutes later, Clark had the final touch as the ball rifled into the net - unfortunately for him it was to divert McGregor's powerful low drive away from and beyond Benji Siegrist.
The Celtic captain had stepped into the area from a short corner and firing into the ruck of bodies assembled in front of him was always likely to produce a decisive deflection.
His call for calm was then answered by his team-mates as Celtic took control. The hosts' outlook wasn't helped by the energetic Ian Harkes succumbing to injury before the 25-minute mark.
He was replaced by Kevin McDonald but the break in play didn't serve to disrupt Celtic's rhythm and intent, although there was perhaps a bit too much vigour in Hatate's challenge on Kieran Freeman, with United disappointed to see the midfielder come away with only a booking.
Celtic had the ball in the net 10 minutes later by Maeda's tap-in was ruled out for handball by Giakoumakis in the build-up, before a marauding McGregor almost picked out the top corner from the edge of the box.
A scramble in the box as Maeda attempted to bustle his way through was the last meaningful action of a half Postecoglou will have been pleased with.
United, however, appeared from the break with renewed intent and they mounted a period of pressure that was escalated by Celtic playing themselves into trouble.
But while the visitors merely flirted with trouble, it was United who suddenly took a hammer to the self-destruct button.
Siegrist should have caught Maeda's harmless cross with his eyes closed but a fatal fumble allowed Giakoumakis to nip in and squeeze home the second.
It was a bitter blow for the hosts given their post-interval improvement, but a lesson in making such spells count.
From there on out, Celtic were comfortable in containing United's threat, or lack thereof, as they huffed and puffed for a way back.
Throwing caution to the wind was always likely to leave gaps going the other way and Celtic waited for the moment to kill the game.
Karamoko Dembele was bright on his introduction from the bench and he was set free down the right by O'Riley with United toiling to recover.
His shot was deflected on its way to goal and helped over the line by Giakoumakis to round off a fine evening for Postecoglou and his team.
3 talking points
Dare to dream of a Treble?
Postecoglou gave a typically measured response to pre-match questions of a Treble by pointing out that the default expectation at Celtic is to win every trophy anyway.
And while that's true, it's an altogether different anticipation the closer it comes to being a reality.
With the League Cup already in the bag, an advantage in the Premiership title race and now a return to Hampden on the cards, expect that excitement to build only further in the coming weeks, should Celtic maintain their current form.
They've certainly settled into a winning habit, negotiating this trickiest of cup ties without hitting top gear or ever being in any serious danger.
They certainly have the squad for it now, too, as this evening demonstrated. With Jota and Abada out, James Forrest was afforded another opportunity and the return of Giakoumakis was a welcome one for the Parkhead side.
Man in the middle
It'd be wonderful to get through a big game without some sort of refereeing flashpoint but, alas, this was not that evening.
Both teams come away in the belief that a big call didn't go in their favour.
First up was Hatate's risky challenge on Freeman, with the Japanese star's studs showing as he attempted to chase the ball down near the touchline.
Referee Beaton brandished only a yellow, deeming there was not enough in it to send the player off.
Minutes later, it was Celtic's turn to feel aggrieved when Maeda's goal was chalked off for a handball in the moments before.
The ball did strike Giakoumakis' arm, but it was one that mirrored a number of incidents down south where the goal was allowed to stand with the judgement that the handball was not deliberate.
United lack cutting edge
Dundee United have already proven they can make life difficult for anyone at Tannadice and there was an early second-half period here where they threatened to give Celtic's credentials a real examination.
But against a side with such potency in attack, periods of ascendency have to be meaningful ones.
Unfortunately for Tam Courts, his team hassled and harried without landing a serious blow on their opponents.
What will agonise the United manager further is they then gifted Celtic a decisive second without really making them work for it.
Siegrist's error was an uncharacteristic one but ultimately it was fatal.
