A penalty from Nadir Ciftci has given Dundee United a 1-0 lead over Celtic after the first half of a Scottish Cup clash in which both sides have been reduced to 10 men.

The match had a slow start as both team looked to get into rhythm, but it soon sprang to life as Calum Butcher and Virgil van Dijk were involved in a fiery challenge on the halfway line.

A melee started between both sets of players, which was only stopped when the assistant intervened as the referee's back was turned.

On his colleague's instructions, Craig Thomson sent off Van Dijk and Paul Paton, despite the latter not being involved in the incident.

United settled the better of the two sides and Ryan Dow was presented with a good chance as he broke away down the right, but he could only scuff his shot at Craig Gordon.

Dundee pressed again and Aidan Connolly was brought down on the edge of the box by Scott Brown. Ciftci took the set piece, but he failed to test Gordon as he dragged his strike wide of the post.

The visitors upped the ante to push back into the match and came close when Stefan Johansen drilled an effort at goal from distance, but Radoslaw Cierzniak made a good save to keep it at bay.

Just before the break, both sides hit the post within seconds of each other as Dow could only guide John Rankin's strike onto the woodwork, while Anthony Stokes was left one-on-one with Cierzniak and beat the keeper, only for his effort to come back off the frame of the goal.

There was further drama to come when Connolly was brought down in the area by Stokes and a penalty was awarded. Ciftci took the spot kick and placed the ball into the bottom corner to put United ahead at the interval.