Inevitably, it all kicked off in the end. Three games in two competitions over 10 days has forged some barely disguised contempt between Celtic and Dundee United. Six red cards tell their own tale. For Jackie McNamara’s team, the frustration — and indiscipline — is growing. Ryan McGowan became the fourth United player to see red in the dying minutes, seconds after Celtic’s Anthony Stokes was dismissed for a retaliatory kick at Paul Paton. Afterwards, Ronny Deila rounded on the Australian, claiming he could have injured substitute Liam Henderson ‘for life’. The open wounds enveloping this fixture are now there for all to see. Virgil van Dijk (left) celebrates with his team-mates as Celtic comfortably progressed on Wednesday . Celtic manager Ronny Deila celebrates at full-time as his side reached the Scottish Cup semi-finals . Anthony Stokes (second left) comes together with Ryan McGowan in the second half . CELTIC: Gordon, Ambrose Emuobo (Fisher 72), Denayer, Van Dijk, Izaguirre, Bitton, Brown, Forrest, Commons (Henderson 80), Stokes, Griffiths (Guidetti 58) Subs not used: Scepovic, Zaluska, Wakaso, McGregor . Goal: Denayer 17, Griffiths 57, Commons 79, Van Dijk 90 . Sent off: Stokes . Booked: Ambrose Emuobo, Izaguirre, Guidetti . DUNDEE UNITED: Cierzniak, McGowan, Fojut, Morris, Rankin, Spittal (Connolly 74), Paton, Butcher, Erskine (Anier 70), Dow (Telfer 70), Ciftci . Subs not used: Souttar, Smith, Szromnik. Spark . Sent off: McGowan . Booked: Cierzniak, Rankin, Ciftci . Referee: Calum Murray . It is hard to see who will stop Scotland’s champions now. United will have a fourth attempt in the SPFL Premiership this weekend. Yet after losing the League Cup Final and crashing out of the Scottish Cup in this quarter-final replay, that prospect holds all the appeal of a cold-meat buffet with Jeremy Clarkson. Inverness Caley Thistle will make all the right noises before a Scottish Cup semi-final at Hampden. Aberdeen believe their title aspirations are alive and well. Yet, Celtic are developing a habit of wrapping themselves around opponents and squeezing tight. For Deila, the fourth domestic Treble in this old club’s history is edging over the horizon. Jason Denayer’s 17th-minute headed goal was the platform for Leigh Griffiths to add a second on 57 minutes. Kris Commons thrashed the third high into the net 12 minutes from time before Virgil van Dijk tapped in from close range in the final moments. By then, things threatened to run out of control. Stokes had taken a kick at Paton and witnessed the flash of red. The crowd bayed for retribution against McGowan seconds later and were duly obliged by referee Calum Murray. In a freakish run of three consecutive meetings, United have now scored one, losing six. They return to Glasgow at the weekend a punch-drunk team blighted by suspensions, with former players Stuart Arsmtrong, Gary Mackay-Steven likely to return to the Celtic fray. It’s hardly a prospect to savour. Deila’s team began the game with a flourish and kept going. Nadir Ciftci, the United striker spared further punishment for a kick to the face of Scott Brown in the first game, felt the Celtic skipper’s robust retribution in all of six seconds. It was a forerunner for what was to come. For one heart-stopping moment in only the second minute, the visitors feared they might witness their latest red card in this fixture when keeper Radoslaw Cierzniak raced from his line to clatter Griffiths as he hared on to a superb Commons through ball. Griffiths had already lost control, the goalscoring opportunity gone. Referee Murray — rightly — contented himself with a yellow card. He would have the chance to flex his muscles later. Jason Denayer (centre) rises above the Dundee United defence to score the opener for the hosts . Denayer celebrates after putting Celtic 1-0 up in the Scottish Cup quarter-final . McNamara reshaped his defence in the absence of suspended duo Paul Dixon and Sean Dillon, fielding midfielder John Rankin as a makeshift, emergency left-back. The midfielder suffered a form of torture here. It made for painful viewing. James Forrest — finally free of injury and a scorer in last Sunday’s League Cup triumph — used his pace to offer Celtic width and speed. Even so, the home team had just one goal to show for 45 minutes of dominance at the interval. It came from a Calum Butcher foul on Commons midway inside the United half. Stokes — an improved performer since his recent disciplinary faux pas — floated the ball into a crowded area, Denayer planting a firm, looping header beyond Cierzniak for his fifth of the season. At Hampden, Celtic were loathe to build on their lead and possession. So it was here again. They had the chances. A Commons corner picked out van Dijk, the Dutchman’s firm header surging over the bar. Celtic's Leigh Griffiths (right) is airborne as he puts his side 2-0 in front against Dundee United . Griffiths gives a salute as he slides across the Celtic Park pitch in celebration . Taunting and tormenting Rankin, Forrest then came close to scoring by accident. Putting his head down and surging for the byeline, his attempted cross dropped under the bar and was heading into the net until Cierzniak tipped over at the last. Another opportunity was passed up before half-time, a sclaffed Cierzniak kick out to Nir Bitton prompting a rare loss of composure in the usually unflappable Israeli. He had the chance to shoot, but opted to take on Callum Morris instead and lost the ball. United’s resistance was sporadic. They came close in 32 minutes after an outstanding incursion down the right flank by McGowan. The Australian made it unchecked from his own half to the Celtic byeline, his low centre aimed at Ciftci before Celtic keeper Craig Gordon managed — unconvincingly — to get a hand on the ball. Kris Commons (second left) scores Celtic's third goal of the evening at their home ground . Commons celebrates as Celtic go three up against Dundee United in the cup . Efe Ambrose, in that way of his, casually walked the ball clear from under his own crossbar. Celtic then began the second period in a ragged, loose fashion and that allowed the visitors their best spell of the game. In the opening five minutes, United summoned more attacking menace than they had managed in the entire first 45. Ciftci’s low, right-foot shot was pushed up in the air by Gordon as he retrieved another piercing ball across the face of goal from McGowan. But it didn’t last long. Until the 57th minute to be precise. Celtic scored with virtually their first effort on goal in the second period, Griffiths cleverly guiding a quite superb long ball from Brown past Cierzniak with a first-time effort from 12 yards. The outcome was placed beyond doubt 11 minutes from time. Commons blew a fine chance after a flowing passing move involving Darnell Fisher, Bitton and a Stokes cut-back. Last season’s Player of the Year — a scorer at Hampden last Sunday — dallied too long. Celtic's Stokes speaks with referee Calum Murray before he is sent off . Celtic's John Guidetti (second right) shows his fury as he comes together with McGowan . McGowan is sent off by referee Murray as both sides end the match with 10 men . Van Dijk scores with a tap-in late on to cap a successful night for the home side . But within seconds he atoned, playing a deft one-two with substitute John Guidetti before slamming the ball high into the net for 3-0. What came next was regrettable, but predictable. Two teams sick of the sight of each other began settling scores. Stokes took a blow to the mouth, drawing blood, and the Irishman took swift revenge as he lay on the deck. Off he went. Within moments, the scores were evened up when McGowan’s crude lunge at substitute Henderson sparked a melee at the corner flag. The former Hearts player went off after what Deila described as a ‘stupid’ challenge — with some verbals between the two as he left the pitch. And Deila’s players had the last word when van Dijk tapped in Denayer’s simple cut back from close range.
Celtic comfortably progressed to the William Hill Scottish Cup semi-finals . Jason Denayer, Leigh Griffiths, Kris Commons and Virgil van Dijk all scored for the hosts at Celtic Park . Both sides ended with 10 men as Anthony Stokes and Ryan McGowan were sent off .