DUNDEE United and Celtic will be sick of the sight of each other soon enough, but others will lap up plenty more if it's the equal of what they delivered in an absorbing, bruising Scottish Cup tie.

The pair of them have begun a strange little affair in which they were due to meet in three consecutive matches. After this, add a replay to make that four. Celtic's prospects of landing the treble were on the ropes against Dundee United until Leigh Griffiths equalised Nadir Ciftci's opener. After that it was United who were hanging on for dear life. Celtic played 80 minutes with ten men. United played 38 minutes with ten and 42 with nine.

It was a mesmerising game, stuffed with incidents and controversy. There were thee red cards, two penalties, a blatant dive, and enough rancour and debate to make SFA compliance officer Tony McGlennan wish he'd taken the week off. Virgil van Dijk and Paul Paton were sent-off after ten minutes - Paton an alarming victim of mistaken identity - while Ciftci, Calum Butcher and Scot Brown could all have got their marching orders at the same time. When Paul Dixon was correctly dismissed for a subsequent handball United had were left facing nearly the entire second half a second man down, and at times it resembled the Alamo.

The relationship between United and Celtic has become tense. That's partly down to them meeting in what will now be four consecutive games - this one, next Sunday's League Cup final, the cup replay on Wednesday March 18, then again in the Premiership three days later - and partly down to Celtic pinching two of United's best players. Stuart Armstrong and Gary Mackay-Steven are ineligible for the two cup ties and it is a credit to how well they have done that Celtic already look poorer without them. Some bad feeling, or at least some tension, was evident in all the niggly little fouls and blocks which pock-marked the game from the start, even before the first two red cards.

Those early dismissals were poor. Assistant referee Graham Chambers got Paton's one spectacularly wrong. Brown came flying into Ciftci and as they tangled Ciftci stuck his boot into Brown's face. Instantly, Butcher came thundering in on van Dijk and the pair lashed out at at each other with their feet. Once the melee had settled the referee, Craig Thomson, took Chambers aside to get his version of events. The conversation went on and on and on, with Thomson seeming to check and double-check what he was hearing. Chambers was both insistent and wrong, a bad combination. Ciftci, Brown and Butcher didn't even get a booking between them for the incident but van Dijk and - shockingly - Paton were given straight reds.

At that point, United reacted better, pushing Celtic back and applying pressure. Ronny Deila pulled Nir Bitton back into defence and Ryan Dow quickly turned him and got in behind, but nothing came of it and United didn't manage it again. Ciftci had a dangerous free-kick and a Butcher shot was deflected on to the post by Dow. It was hard to remember a half in which Celtic created fewer chances this season. Not until Anthony Stokes hit the post, when he should have scored, did they threaten.

Mistakes gave United their lead just before the break: a mistake by Celtic, a mistake by the referee. Emilio Izaguirre gave the ball away at the touchline and Aidan Connolly burrowed his way into the box, riding a couple of challenges but then diving when Stokes came in on him. Thomson bought it and gave a penalty. Jackie McNamara has told Ciftci he must learn how to control his aggression but there are times when looks like he has ice in his veins. The huge Celtic support tried to put him off as he took his kick, then watched him bury it right in the corner, cool as you like.

All of this made for a scrappy and fractious game, careering around on a bad pitch. It was compelling from start to finish, especially when United had another man sent off three minutes into the second half. There was some controversy around it, too, but Dixon raised his arm when blocking Griffiths's shot and that was a penalty and red card. United lost their left-back but not their lead. Griffiths's kick was saved by Radoslaw Cierzniak, who had a great match, and the rebound was hacked away. Twenty minutes later Cierzniak delivered another terrific save with his legs to deny substitute John Guidetti. By then the game had changed entirely, into almost uninterrupted waves of Celtic attacks and desperate United defending. There was too long for them to hang on and after 23 minutes with nine men their resistance broke when Stefan Johansen crossed and Griffiths shaped his body beautifully to place a great header back across goal and into the corner.

United's passing often let them down as they tried to relieve the pressure and Celtic's final balls and decision-making weren't anything to write home about either. Both of them came through a test, though. Celtic's hopes of the treble survived. United played for half the game with nine men but are still in the cup. Three more like this? Bring them on.