Griffiths at the double as Celtic hammer United

The Scotland striker opened the scoring in the 21st minute when he drilled a low drive through the legs of United 'keeper Eiji Kawashima to notch up his 50th goal for the Hoops.

Jozo Simunovic heaped more woe on United in the 27th minute as he headed home his first Celtic goal before Simon Murray pulled one back for United four minutes later.

Griffiths restored Celtic's two-goal advantage in the 48th minute and Kris Commons volleyed home a sizzling fourth just eight minutes later as the reigning champions eased to victory over United, who remain 11 points adrift at the bottom of the table.

The result extends Celtic's winning run to three games and puts the pressure on second-place Aberdeen who travel to Dingwall to take on Ross County on Sunday.

There were five changes for United from last weekend's Scottish Cup win over Airdrieonians while Craig Gordon, Australian midfielder Tom Rogic and former United player Stuart Armstrong all returned for Celtic.

Armstrong and Commons came close for Celtic before Rogic set up Griffiths to open the scoring in the 21st minute. The Socceroos star evaded two tackles before dinking a deflected pass into the path of Griffiths who took a touch before firing between Kawashima's legs.

Griffiths was in an offside position at the goal and United's problems got worse six minutes later as Simunovic beat Japanese international 'keeper Kawashima to connect with Commons' free-kick and bullet home a free header.

United were thrashed 5-0 by the Hoops back in October and a similar result looked to be on the cards before a rare goal from Murray, who was only playing due to the absence of top scorer Billy McKay on compassionate leave, hauled the home side back into contention in the 31st minute.

John Souttar surged forward and slipped a fine through ball for Murray who flicked a shot with the outside of his right foot past Gordon.

Gordon then came to Celtic's rescue as he blocked a close range effort from Australian defender Ryan McGowan on the line as half-time loomed.

An explosive start to the second half saw Kawashima push a powerful free-kick from Commons round the post.

United then had an appeal for a penalty turned down after Murray and Gordon collided in the box before Celtic raced up to the other end to restore their two-goal cushion in the 48th minute.

Mikael Lustig's low cross reached Griffiths in the inside left channel of the box and he blasted the ball low past Kawashima with his weaker right foot.

The United 'keeper then made two fine saves to deny efforts from Griffiths and Callum McGregor but could do nothing to prevent Commons making it 4-1 in the 56th minute.

United's Scott Fraser was easily dispossessed in midfield allowing Armstrong to curl a cross to the far post where Commons rose to fire a sensational scissor-kick high into the net past Kawashima.