Full-time at The Cherry Red Records Stadium
Lions boss Neil Harris named a strong starting line-up at Wimbledon, including a first outing of pre-season for David Forde.
The Lions had an early let-off when a free-kick from Sean Rigg was headed just over by Will Nightingale.
On 13 minutes, there was concern in the Lions dug-out as Aiden O'Brien went down under a heavy challenge and after being helped off required a stretcher to take him to the dressing room.
No sooner had Kris Twardek replaced him than former Lion Lyle Taylor latched onto a through ball to put The Dons in front.
On 27 minutes Millwall launched a promising break with John Marquis running at the heart of The Dons defence but his delayed pass to Fred Onyedinma allowed the home side to smother the danger.
Nine minutes later Byron Webster went close with a shot tipped over the bar by James Shea following a corner.
Marquis then saw a header blocked from a Shaun Cummings cross as Millwall finished the half strongly, but went in at the break a goal behind.
Jordan Archer replaced Forde in goal and The Lions started the second half brightly, with Shaun Williams drawing a fine save from Shea following a short free-kick taken by Joe Martin.
Another ex-Lion, Karleigh Osbourne then went close at the other end with a header from a corner.
Onyedinma continued to look a threat on occasions and was unlucky to be denied with a last ditch challenge as he ran through.
Millwall forced a series of corners midway through the half and from one of them Marquis flicked an effort just wide.
Ed Upson then brought the best out of Shea on 75 minutes as The Lions continued to press for an equaliser following a plethora of substitutions by both sides.
Twardek saw a shot deflected wide following yet another corner as The Dons battled to hold onto their lead. The home side were then reduced to ten men with Azeez hobbling off after all their subs had been used.
Millwall's pressure finally told right at the death as Sid Nelson headed the equaliser following a corner by Jack Powell.
Wimbledon: Shea (McDonnell 81mins), Fuller (Pilbeam 71 mins), Osbourne (Sweeney 71mins) Meades ( Bulman 64 mins), Nightingale (Harrison 77mins), Barcham (Kennedy 64mins), Francomb (Beere 64mins), Reeves ( Toonga 64 mins), Elliott (Azeez 60 mins), Taylor (Akinfenwa 46mins), Rigg (Fitzpatrick 60mins).