Ryan McGowan and Ronny Deila exchange words after the United defender was sent off.

The "dream is still alive" for Ronny Deila and Celtic after they beat Dundee United 4-0 in a Scottish Cup quarter-final replay to stay in the hunt for a domestic treble.

Goals from Jason Denayer, Leigh Griffiths, Kris Commons and Virgil Van Dijk set up a Hampden semi-final with Inverness Caledonian Thistle next month.

Anthony Stokes was also sent off for lashing out at Paul Paton, with United's Ryan McGowan red carded minutes later for a challenge on Liam Henderson.

"A great performance and a good victory, an important victory," Deila told BBC Scotland.

"The dream is still alive. We are in the semi-final now and that is nice.

"I think we showed we have a tempo that is very hard to cope with."

There have now been six red cards in the three consecutive cup ties between the two sides, ahead of Saturday's Scottish Premiership encounter.

"It is too much but it is how it is," continued Deila. "It's tense, there is a lot of energy and it's easy to get angry, so that happens.

"It's about a trophy, and a quarter final. Everybody is very up to win, and sometimes you lose your head."

Ronny Deila celebrates at full-time after Celtic made the Scottish Cup semi-final.

Dundee United assistant manager Simon Donnelly also felt the refereeing had been harsh over the course of three games.

"It's astonishing," said Donnelly. "I think it's the current game. I've certainly been involved in a lot more robust games over the years than the three that we've watched.

"I've not seen the McGowan tackle at the end. I've had reports it's a good, strong tackle. I think the reaction of the Celtic players on the back of them just having a red card possibly influences the referee, but I'll need to see it again.

"I don't think the games have been dirty. There's been incidents in all three games. I don't think there's been six red cards in the three games."

Celtic host Dundee United again on Saturday, and Donnelly called for an improvement after conceding what he called "soft" goals.

He said: "It's going to be tough again. We're going to have to defend a lot better that's for sure, Celtic are really dangerous on set plays and that's proved costly again tonight."