MAXI Gradel's second-half double continued Cherries' fine run of home form, as Kevin Bond's charges added to Millwall's relegation fears at Dean Court.
And with Crewe losing 2-1 at Luton, Cherries' 12-point deficit is now down to nine points.
Bond's men have now racked up four consecutive home wins in the league for the first time in four years as their seemingly impossible battle against the drop continues.
Gradel's 74th-minute penalty after Sam Vokes had been pulled down by Lions captain Paul Robinson put Cherries on their way, before the Ivorian's fine individual effort with one minute remaining sealed the points for Bond's men.
But it was Cherries keeper David Forde who will take most of the plaudits after he turned away Neil Harris's spot kick just after the hour mark.
It was Cherries' first victory against the Lions since their League One win at Dean Court 12 months ago, following two defeats at the Den earlier this season.
Billy Franks dropped to the bench after his exploits against Tranmere Rovers on Easter Monday, with Josh Gowling returning to Bond's back four.
Vokes returned from international duty with Wales under-21s to spearhead Cherries' attack, while Jo Kuffour missed out on compassionate grounds.
In a dire first half where chances were at a minimum, both sides struggled in conditions more akin to the Scottish highlands than the glorious south coast.
Shaun Cooper's free kick after two minutes failed to trouble Lions keeper Rhys Evans, after Richard Shaw had chopped down Marvin Bartley on the edge of the Millwall box, while Tony Craig was lucky to escape a booking after felling Gradel 10 minutes in.
Harris went close after a quarter-of-an-hour, but the Lions striker's athletic bicycle kick was nicely tipped over by Forde.
Forde then got down well to his left to beat away David Martin's 29th-minute drive, before referee Paul Melin booked Martin for a foul on Bartley - despite the former Hampton and Richmond man appearing to hand-off' the Lions midfielder in the face.
Lee Bradbury's 34th-minute curler and Jay Simpson's right-foot effort a minute later at the other end both fizzed wide as both sides upped their search for an opener.
Simpson then hit the side netting with a well-struck drive from the corner of Forde's penalty area with six minutes of the first half remaining, while Josh McQuoid's cross on the stroke of half-time was just too far in front of the advancing Gradel and Vokes.
Gowling's precision pass put Vokes through four minutes after the restart, but Evans was quickly off his line to get down at the feet of the Lymington-based teenager and gather safely.
Substitute Brett Pitman latched on to Vokes's incisive through ball on 53 minutes, but the Channel Islander's sublime finish from the edge of the box was ruled out for offside.
Cooper came to Cherries' rescue 10 minutes into the second period when he cleared Craig's header off the line with Forde well beaten.
Danny Hollands's dipping free kick from wide on the right caught Evans by surprise, but the Lions keeper did well to turn the ball away for a corner on the hour mark.
Then former Cherries loanee Jem Karacan, anonymous for much of the clash, crashed to the turf under Cooper's challenge moments later and referee Melin pointed to the spot.
It seemed harsh on Cooper, with contact appearing minimal, but justice looked to have been done when Forde guessed right to parry Harris's penalty into the path of substitute Armet Brkovic.
Brkovic, however, sliced his shot wide with Forde grounded and the goal gaping.
The Croatian almost made amends moments later but an inspired Forde tipped his 25-yard free kick over the bar.
As the clash finally came to life, Pitman's spectacular half-volley from just outside the Lions box rattled Evans's left-hand upright, before Cherries won their own spot-kick with 16 minutes left on the clock.
Vokes was hauled down by Robinson when attempting to get on the end of Pitman's teasing cross and Gradel, who missed from 12 yards against Gillingham a week ago, stepped up to smash the ball past the sprawling Evans.
Cherries had another shout for a penalty waved away by Melin after 85 minutes when debutant Steve Hutchings, on as an 83rd-minute substitute for Vokes, looked to have become the second victim of a Robinson push.
Hollands right-foot drive with three minutes remaining failed to trouble Evans, before Gradel's moment of magic with a minute remaining made the points safe for Bond's troops.
The Leicester loanee picked up the ball wide on the left, before weaving his way into the Lions box, passing two men and drilling the ball past Evans deep into the far corner.
Cherries: (4-5-1) Forde 8*; Bradbury 7, Gowling 7, Cooper 7, Pearce 7; Gradel 7.5, Hollands 7.5, Bartley 7, Tessem 6 (Pitman, h-t) McQuoid 7.5 (Partington, 68); Vokes 7.5 (Hutchings, 83).
Unused subs: Franks, Pryce (g/k).
Booked: Hollands.
Millwall: (4-4-2) Evans; Senda, Robinson, Shaw (Gaynor, 88), Craig; Simpson, Fuseini, Karacan, Martin; Harris, Savage (Brkovic, 61).
Unused subs: Bignot, Cochrane, Pidgeley (g/k).
Booked: Martin.
Referee: Paul Melin.
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