Millwall booked their place in the First Division play-offs in style as Dion Dublin and Neil Harris combined to secure an impressive victory against Grimsby at The New Den.

The Lions went into the match knowing a point would be enough to cement a top-six spot and keep their hopes of promotion to the Premiership alive.

And three first-half goals meant there was never any chance of Mark McGhee's men relying on results elsewhere as they set up a play-off semi-final against Birmingham.

Any nerves Millwall might have had before kick-off were soon eased when they took the lead in the fifth minute with the first meaningful attack of the match.

Matthew Lawrence's cross from the right found Dublin and the on-loan Aston Villa striker tucked the ball home to send the home fans into raptures.

But Grimsby equalised six minutes later when Danny Butterfield chested down Stacey Coldicott's pass and tucked the ball past Tony Warner to silence the home crowd.

Millwall looked determined to attack rather than try to hang on for the draw and Dublin was continuing to cause problems for the visitors' defence but saw a header saved by Danny Coyne.

Grimsby's Iain Ward was the first player to go into the referee's notebook when he was shown the yellow card for a foul on Steven Reid before Dublin again tried his luck with a header but was unable to hit the target.

The home side were beginning to dominate and Stuart Nethercott headed over from Reid's corner before Harris' curling shot was brilliantly saved by Coyne.

Dublin turned from goalscorer to provider in the 27th minute as the Lions recaptured the lead that their play deserved.

The former England international found strike partner Harris and Coyne was unable to keep out his header despite getting a hand to the ball.

Dublin helped out in his own penalty area moments later when he cleared Cooke's corner and the Londoners doubled their advantage when Dublin again set up Harris to volley home the third just after the half-hour mark.

Harris threatened to complete a first-half hat-trick but headed over from David Livermore's cross and then shot wide with a left-foot volley.

Millwall suffered a setback when Dublin failed to appear for the second half and was replaced by top scorer Steve Claridge.

Grimsby made a bright start to the half, with Michael Boulding's shot from just inside the area forcing a save from Warner, and Millwall had Matthew Lawrence booked for a foul on Paul Robinson.

Warner was also called upon to keep out a well-struck effort by Butterfield just after the hour but chances were few and far between as the hosts looked happy to hold onto their two-goal advantage.

To their credit Grimsby continued to battle as they searched in vain for a lifeline and late shots from player-manager Paul Groves and Robinson were dealt with comfortably by Warner.

Harris and Claridge were both brought off in the closing minutes as Millwall turned their attention to the play-offs.

Teams

Millwall Warner, Lawrence, Nethercott, Ward, Bull, Ifill, Cahill, Livermore, Reid, Harris (Bircham 89), Dublin (Claridge 45), Claridge (Ryan 89).

Subs Not Used: Gueret, Dyche.

Booked: Lawrence.

Goals: Dublin 6, Harris 23, 31.

Grimsby Coyne, Ward (Burnett 63), Groves, Todd, Chapman, Cooke (Robinson 50), Coldicott, Pouton, Butterfield, Boulding, Allen (Livingstone 76).

Subs Not Used: Croudson, Raven.

Booked: Ward.

Goals: Butterfield 11.

Att: 17,004

Ref: A Butler (Sutton-in-Ashfield).