Watch highlights of Town 1 Millwall 2
Watch the match highlights of a sucker punch for Shrewsbury Town as Millwall came from behind to take all three points.
James Collins gave Town a 55th minute lead but it was quickly cancelled out as Steve Morison (59) equalised before Lee Gregory's 67th-minute penalty sealed it.
Substitute Liam McAlinden wasted a golden chance to level in the 85th minute and Town went close with first-half headers from Tyrone Barnett and Jean-Louis Akpa Akpro.
But Millwall deserved their win after Jayson Leutwiler saved from Shaun Williams, Fred Onyedinma and Lee Martin, while Abu Ogogo headed off the line from Mark Beevers, all before the break.