His manager's arm around his neck and the match ball in his hand after his second hat-trick in four matches, Leigh Griffiths left the Tannadice pitch knowing he had edged Celtic ever closer to a successful defence of their Premiership title yesterday.

As against Kilmarnock 11 days earlier the striker's intervention both tellingly contributed to and reflected a transformed performance by his team in the second half of a match they had struggled before the interval to impose themselves upon.

"If you'd asked me at the turn of the year if I was going to be our top goal-scorer with five games to go I would have laughed at you, but it shows how hard I've worked and I've changed the manager's mind about me as a player. I'm reaping the reward now and so's he," said Griffiths.

Both looked delighted and Ronny Deila who, after that previous hat-trick, praised the player's response to having been told what is expected of him, went further this time in indicating that he may even be the man to lead the line when Celtic return to European action early next season.

"I'm not afraid of that," he said.

"He's shown that he can score goals and if he can just continue working hard he'll score goals in Europe as well."

Given the relative ease with which Celtic had been brushing United aside by the time they got towards the end of their epic sequence of four successive encounters which filled their March schedules, however, yesterday's first half had been a rather different matter.

Such was the balance of play it was tempting at half-time to ponder what might have been had Jackie McNamara, United's manager, decided when Stuart Armstrong and Gary Mackay-Steven were sold to Celtic in January, to trust the next generation a bit sooner.

Introducing Robbie Muirhead and Blair Spittal up meant there were four teenagers in United's starting line-up, representing something of a different approach to the safer looking options he took last month when understandably seeking to consolidate after his team's form deserted them in the wake of those sales.

The vitality of yesterday's first half performance, Spittal, Muirhead and their fellow teenagers Charlie Telfer and John Souttar all performing well, consequently invited consideration of whether it might have been better to see those departures as a chance to inject fresh blood rather than relying on players whose greater worldliness might make them more aware of the implications of losing such talent so soon after Ryan Gauld and Andrew Robertson had also left them.

That said United's youngsters got a lesson in the importance of remaining focused in the way Celtic, invigorated by half-time discourse, came at them immediately after the break.

Given too much time on the ball in and around the penalty area Scott Brown and Stefan Johansen seized the chance to craft the room for the latter to slide the ball into the path of Griffiths, 12 yards out on the right and the ferocity of his right-footed shot gave Rado Cierzniak no chance.

"First half I thought we were very good, but to concede so quickly after the re-start was disappointing," Jackie McNamara, United's manager, observed.

"It settled Celtic down. You could see them growing in confidence and we went the opposite way. We got deeper and were a bit more nervous on the ball. We stopped doing the things we were good at in the first half with our shape and discipline."

"We had four teenagers starting today and in the first half they went toe to toe with them. We have to learn about concentration. There were some good things but we have to be a wee bit stronger."

From that point it was a different game.

Craig Gordon, Celtic's goal-keeper, having pulled off the best save of the first half in reacting gymnastically to a snap-shot by Muirhead from 25 yards out, Cierzniak demonstrated his ability with fine saves from a Kris Commons diving header, earning instant plaudits from his opponent and a powerful Johansen shot.

The second duly came though when, straining to beat Virgil Van Dijk to a corner sent in from the right, Callum Morris almost registered an own goal, his luck running out as the ball rebounded to Griffiths who poked it towards the line, which it crossed first time, albeit after Cierzniak pushed it out, he knocked it in a second time for good measure.

Then came the penalty decision that could not have been more ironic had Ian Hislop and Ben Elton collaborated on the script as Celtic were wrongly awarded a penalty.

John Rankin candidly admitted to having deliberated cut former team-mate Mackay-Steven down with a nasty looking challenge, his studs clattering heavily into the back of the replacement's leg, but television pictures fully supported his contention that he had ensured the collision happened a couple of feet outside the box.

All the more was that Willie Collum, the match referee, reacted almost like a Rolland Garros umpire leaping out of his seat to check a line call, in going down on his haunches to examine what he thought was the point of contact, before apparently explaining to Rankin he had "been told" it was inside the box, leaving the midfielder to conclude that an assistant referee made the call.

Either way Griffiths seized the chance to persuade Commons, Celtic's regular penalty taker, to let him take the kick and duly sent Cierzniak the wrong way in firing it left-footed to the goal-keeper's left to round off his hat-trick and the win.