A WEEK that began in controversy ended in comfort as a Leigh Griffiths hat-trick inspired Celtic to a comfortable three points at Tannadice this afternoon.

Griffiths' second-half trio - his second hat-trick this month - enabled Celtic to round off their week by taking six league points out of six. The ribbons for the league Championship trophy are all but tied on.

Yet, for all that the scoreline lends an effortless air to the outcome of this contest there was a pedestrian look to Celtic in the opening 45 minutes. It was only after the break that Ronny Deila's men were able to up the tempo and dominate their hosts.

Given the frequency with which the sides have faced one another recently and the controversies that those games have given rise to - this was the seventh time this season and the fifth time in the past month - there was fair bit of niggle between the players in the early stages.

Hoops captain Scott Brown found himself in the book for a challenge on John Rankin shortly after the half-hour mark, but in many respects his foul was symptomatic of the frustrations within the Celtic side.

Virgil van Dijk who had the two best chances of the opening period underlined Celtic's reliance on set-pieces to open up the United defence. The Dutch defender had one header that looped over the bar and another deflected snapshot that was straight into the arms of Radoslaw Cierzniak.

At the other end Robbie Muirhead - who enjoyed a fruitful afternoon up against Jason Denayer -had a rasping drive that was tipped over the bar by Craig Gordon.

Immediately after the restart, however, Celtic found an opening that would subsequently prove to be insurmountable for United.

Former Tannadice midfielder Stuart Armstrong fed Brown in the box. The Hoops skipper slipped the ball to the feet of Stefan Johansen who in turn teed up Griffiths who rifled his shot low into the bottom right-hand corner.

The goal appeared to energise Celtic who almost doubled their advantage shortly afterwards when Kris Commons header was parried by Cierzniak.

It was a stay of execution for United who found themselves looking at a 2-0 deficit just after the hour-mark. Confusion reigned about the goal, with Griffiths finally getting the final touch.

A Commons' corner had caused chaos in the Tannadice defence when Van Dijk's header had come off the post, Griffiths appeared to bundle the ball over the line before Cierzniak clawed it away and the Celtic striker buried the rebound.

Whistler Willie Collum deliberated before consulting his assistant and awarding Celtic their second of the afternoon.

Gary Mackay-Steven, who had replaced Armstrong, rattled the crossbar after being set up by Ambrose but Celtic put a gloss on the win shortly afterwards when the winger bore down on goal only to be upended by Rankin.

The infringement appeared to be outside the box but from the subsequent spot-kick Griffiths netted his third to claim a hat-trick and 18th goal of the season.

The Tayside theme continues this week with Celtic facing Dundee at Celtic Park on Friday night.