Full-time from the Crabble Athletic ground
The game saw Shane Ferguson handed his first start since returning from international duty at Euro 2016 with Northern Ireland and join the likes of Fred Onyedinma, Gregg Wylde, Tom King and Sid Nelson in The Lions starting line-up.
Dover carved out the first scoring chance of the game with barely 60 seconds on the clock when Tyrone Marsh's 20-yard free-kick from a central position flew narrowly over the bar.
The Lions, operating with Onyedinma and Jamie Philpot up top with Wylde and Kris Twardek taking care of the left and right wings respectively, got little change from an organised Dover rearguard.
It was the home side who looked the more likely to score, certainly in the opening half, with a couple of teasing deliveries from the right from Ricky Modeste inches flashing across the face of goal.
Jim Stevenson's left-foot curler on 24 minutes forced a smart save from keeper King, who pushed the striker's effort over the bar, whilst at the other end, Paul Rooney was a whisker away from breaking the deadlock just five minutes later. Winning the ball in midfield with a crunching challenge, the powerfully-built centre-half weaved his way into the left side of the penalty area before taking aim, only to see his low effort flash a foot wide of the upright.
Rooney snatched at his shot four minutes before the break after Sid Nelson had flicked on Kyron Farrell's corner before Modeste nearly squeezed the ball home for the game's opening goal for Dover, but fired into the side netting as the opening half came to a close.
Lions skipper Nelson was the first player to try their luck on goal a couple of minutes after the restart when he played a neat one-two with Brown, strode forward and let fly from 20-yards with a low skidder that flashed past the post.
Nelson was in defensive action moments later, making a crucial sliding tackle to avert the danger as Modeste threatened to break clear on goal.
The home side enjoyed a little spell of pressure with two corners in quick succession dealt with by Millwall, but when a Dover third corner was whipped in on 63 minutes, Ferguson inadvertently flicked into the path of Miller and the frontman was on hand to nod home beyond the reach of King.
Seconds later a trio of Lions subs - Alfie Pavey, Harry Smith and Noah Chesmain - entered the fray having been waiting patiently on the touchline to come on prior to Dover's opening goal.
Trialist Smith was unable to get on the end of Farrell's deep delivery as Millwall tried to force a way back into the game, but it could so easily have been 2-0 to Dover on 65 minutes when Miller slipped a neat ball in to Stevenson, whose low shot was well held by King in the visitors' goal.
Dover had the bit between the teeth and some solid defending by right-back Brown prevented Miller from connecting with the ball 16 yards out and a super save at full stretch by King denied Stevenson as the home side kept their foot on the gas.
Harris shuffled his playing pack with just under a quarter of an hour to go, bringing on Danny McNamara in a move that saw right-back Brown switch to the opposite flank and left-back Chesmain move further up field in place of Wylde. Rian Bray then came on for Nelson, but the sub barely had time to take his position as The Lions defended a free-kick, whipped in by Mitch Pinnock and headed home by Grimes to make it 2-0.
McNamara's mazy late run was brought to a halt by a clumsy challenge, but the resulting free-kick flew wide and summed up what was a disappointing night for the south Londoners.
Scorers: Miller (61mins), Grimes (81mins)
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