Second-half goals from Andy Keogh and Martyn Woolford booked Millwall's place in the Capital One Cup Second Round draw at the expense of League Two battlers AFC Wimbledon.
Keogh kept his cool to fire home from the tightest of angles to break the deadlock on 51 minutes and Woolford looked to have put the result beyond doubt for Millwall with a second from close range with 12 minutes remaining.
But Luke Moore smashed home in the 89th-minute to set up a nervy four minutes of injury-time - and it took a stunning save by debutant Stephen Bywater to deny sub Jack Midson a leveller for the visitors right at the death.
Victory was, however, no less than Millwall deserved as they produced a thoroughly professional performance to deny The Dons the opportunity of a Cup upset.
Manager Steve Lomas made seven changes to the side beaten at home by Yeovil on Saturday with Stephen Bywater handed a debut in place of injured keeper David Forde, Jermaine Easter, Scott Malone, Nicky Bailey, Woolford, Paul Robinson and Jack Smith all named in the starting line-up.
In a quiet opening half the best chances fell to Easter, himself making his third 'debut' for The Lions after joining in the summer from Crystal Palace.
Easter was denied by the athleticism of Dons keeper Ross Worner, who clawed his curling effort out as it headed towards the top corner and moments later fired straight into the keeper's hands following another incisive pass from the impressive Bailey.
Both Bailey and James Henry tried their luck from distance, only to see their efforts fly over the bar and Malone sliced wide at the far post from another Bailey delivery as Millwall finished the half in the ascendency.
The Lions continued to dominate after the break, but it took an error by Dons keeper Worner to give Lomas' charges a helping hand when he dithered on the ball, enabling Keogh to nip in and slot home from an acute angle.
Woolford then fired four efforts in quick succession that were blocked by The Dons defence as he became increasingly influential on proceedings.
His persistence paid off after 78 minutes when the industrious Easter took advantage of more hesitancy in the visiting defence and squared for Woolford to lash home at the far post.
That should have been that, but back came Wimbledon and Moore ensured that it was a nervy finale when he slammed a low shot beyond the reach of Bywater after a flick-on from Charlie Sheringham.
Keeper Bywater, who had been a virtual spectator until that point, came to the rescue in the dying seconds with a save at full stretch to push Midson's goal-bound effort to safety as Millwall booked their place in Thursday's Second Round draw.
Millwall: Bywater, Smith, Malone, Bailey (Wright, 70mins), Robinson, Beevers, Woolford, Abdou, Henry (Martin, 74mins), Easter, Keogh (McDonald, 78mins). Subs not used: Gerrar, Feeney, N'Guessan, Osborne.
Keogh (51mins), Woolford (78mins)
AFC Wimbledon: Worner, Fuller, Kennedy, Sweeney (Arthur, 56mins), Frampton, Bennett, Francomb (Midson 56mins), Pell, Sheringham, Moore, Porter (Moore, 70mins). Subs not used: Brown, Fenlow, Smith, Midson, Strutton.
Scorer: Moore (89mins)
Att: 4, 443 (away 1,051)