And the same player wins a penalty for Celtic, though TV replays show that Willie Collum has made the wrong decision - the tackle by John Rankin on Mackay-Steven was just outside the area.

Gary Mackay-Steven crashes a left-foot shot off the crossbar. Celtic are hungry for more.

BBC Scotland football pundit Pat Bonner

"The first half was a good performance from Dundee United. They'd have been disappointed that half time came because they'd be worried they lost their momentum. That's what happened and you get that with young players. That's where they fell down in the second half."

Here's a response from Dundee United manager Jackie McNamara: Aidan Connolly comes on for Blair Spittal.

Dundee United knock the ball about in midfield and win a corner when Virgil van Dijk slices Robbie Muirhead's ball into the box high ball out of play. The set-piece, though, comes to nothing for United. What can the Terrors do to salvage something in the final 12 minutes?

Image source, SNS

Leigh Griffiths, scorer of two goals this afternoon, takes the acclaim of the Celtic fans behind the goal, as skipper Scott Brown comes in to offer his congratulations, one assumes.

Andi Hamilton on Facebook: "7 meetings this season and you can tell, very dull game, a poor celtic side by all accounts, Lenny would have wrapped up the title weeks ago especially with no Hibs, Hearts and Rangers."

Stefan Johansen receives treatment after landing awkwardly from a challenge by John Rankin. The Norway international looks to have winded himself and groggily hobbles off to be replaced by Celtic winger James Forrest.

Just a shade more than 20 minutes left at Tannadice. The Celtic fans are chanting that they are going to win the league.

Alistair Coote replaces Charlie Telfer for United.

Efe Ambrose comes on for Celtic team-mate Adam Matthews.

Goalkeeper Radoslaw Cierzniak is, eventually, beaten for a second time this afternoon as Leigh Griffiths turns the ball over the line from close range, after Virgil van Dijk, competing in the air with United's Callum Morris, heads an effort off the post.

BBC Scotland football pundit Pat Bonner

"Dundee United just don't look as if they are the same team they were in the first half."

Ronny Deila makes a change to his Celtic team: Gary Mackay-Steven replaces another former United player, Stuart Armstrong, a switch that will induce boak in the gullet of some fans of the men in tangerine.

The visiting fans rub their hands as Virgil van Dijk lines up a free-kick from 25 yards. The Dutch defender has been pinging them into the top corner of goals around the country of late but this time he tries a low shot...which evades the wall and slips past the United keeper's right-hand post.

Celtic are enjoying themselves in the Tayside sunshine as Stefan Johansen, in a central position 20 yards out, applies the finishing touch to a move down the right, only for the impressive Radoslaw Cierzniak to make a good save to his right.

Kris Commons pivots on his right foot to power a left-foot shot low at the United goal but the home keeper is down quickly to smother it. United are not finished in this game, though. Their appetite for attack is far from sated.

John the Arab from Tayport: "Scott Brown should have been sent off. It was a shocking tackle on John Rankin, his studs were up. It's a total disgrace. "

Stefan Johansen clips in the type of cross you dream about - using the outside of his left boot from the right touchline - and it lands on the bonce of the on-rushing Kris Commons who got in ahead of Ryan McGowan to power a header towards the top corner of the net. However, there was Radoslaw Cierzniak to leap to save Celtic going two ahead.

United are trying to get a grip on the match again but Celtic have their tails up and are showing a hunger to clinch these three points as they home in on the title.