Lukas Jutkiewicz's 15th minute header against the run of play promised to relieve the pressure on Bolton boss Dougie Freedman, with the Trotters sitting just above the relegation zone.
Millwall's persistence paid off however, and Martyn Woolford struck late on to give the home side a vital share of the points.
The home side did start the brighter too, with Jermaine Easter trying to work an opening within the first five minutes but being stifled well just before pulling the trigger.
Easter shot wide just minutes later after Ed Upson's lofted through-ball to Steve Morison was narrowly cleared.
Medo had Bolton's first chance, but when well-placed just after 10 minutes, his shot was horribly miscued.
Having weathered the early onslaught though, Bolton struck first blood on the quarter hour mark.
Chris Eagles' pinpoint cross created havoc in the Millwall area, allowing Jutkiewicz to head home.
Millwall continued to press thereafter, and nearly found an equaliser just five minutes later when Martyn Woolford's excellent pressure forced an opportunity, but David Wheater was on hand to clear off the line.
Upson was perhaps the brightest spark for Millwall all evening, and continued to create problems for the Bolton defence, with a penalty appeal being waved away in the 24th minute.
Another Millwall effort was cleared off the line a minute later, with Easter denied this time by Alex Baptiste.
Adam Bogdan did well to deny a quickfire Woolford double in the 27th minute - the first a corner nearly taken all the way in by the wind - as Millwall continued to press forward.
Lee Martin came close to drawing the Lions level on the stroke of half-time, but he lashed his effort over the bar when played in by Morison.
The second started with the same pattern as much of the first half, with Morison heading over within minutes of the restart from a corner.
They were nearly two down after 52 minutes however, after Upson was booked for felling Mark Davies, with Eagles' free-kick rebounding back off the post.
Scott McDonald's cross on 66 minutes was nearly turned home by second-half substitute DJ Campbell, but again Millwall's finishing was called into question as the striker headed over.
The miss was nearly punished to the full, when defender Baptiste slotted home on 67 minutes, only to be denied by the offside flag.
Woolford enjoyed a bright afternoon and very nearly dragged his side level on 74 minutes with a venomous strike, but Bolton keeper Bogdan did excellently to keep it out.
Bolton and Jutkiewicz spurned the opportunity to put the seal on all three points with a penalty on 77 minutes after Danny Shittu's handball, but David Forde saved and held onto the ball to keep the home side in with a chance.
It was a chance they took with both hands just five minutes later, with Woolford firing home from an angle to earn Millwall a much-deserved point.