Full-time from The Den
Neil Harris' charges were excellent value for the points too, taking a fourth-minute lead through Abdou and then forcing home their advantage with clinical finishes from Williams (44mins) and Morison (60mins) after former Lion Peter Vincenti had temporarily got Dale back on to level terms with a 43rd-minute equaliser.
The victory was a massive boost to the home players and fans, who were able to enjoy a gutsy display that incredibly secured Millwall's first home win on a Saturday since October 2014.
The Lions started as they have so often this season, on the front foot, determined to get the opening goal and push on to victory.
Harris' men had to wait just four minutes to make the breakthrough with a goal that owed as much to Morison's persistence as it did the skill of Aiden O'Brien and finishing of Abdou. Morison did superbly to intercept a flat clearance by Dale keeper Josh Lillis and spread the ball to strike partner O'Brien. The latter's cross was expertly turned home by Abdou from close range.
Morison was involved again five minutes later with a cushioned header to play Ferguson in down the left, but the Northern Ireland international's delicious delivery was headed behind at the near post for the first of two Millwall corners in the opening half.
At the other end Tom Kennedy's deep cross was comfortably held by Lions keeper Jordan Archer as Dale pushed forward on a rare first-half attack.
The inter-play between Millwall's front men nearly carved out a second goal on 24 minutes. Fred Onyedinma started a sweeping move down the right, touched the ball to O'Brien who worked the ball to Williams via a deft flick from Morison. Williams let fly with a piledriver that was blocked.
Archer came to The Lions' rescue on 28 minutes, superbly turning a Vincenti drive round the post and Abdou did brilliantly to retrieve the ball and avert the danger after an uncharacteristic error from the usually faultless Carlos Edwards.
Morison did supremely well to create a half-chance for Abdou five minutes before the break, but the midfielder just couldn't connect with an inviting low delivery across the face of goal and the ball spun away.
The visitors stunned The Den faithful just three minutes later when they hauled themselves back on level terms with a goal out of the blue courtesy of Vincenti's header from close range following a Joe Bunney cross.
But The Lions responded superbly and restored their advantage just 60 seconds later with a cracker from Williams, whose deft footwork bamboozled the Dale rearguard before he thumped the ball into the roof of the net from 12 yards following another assist from O'Brien.
It was a perfect pick-me-up going into half-time and although Dale forced a bit of a scramble in penalty area during the opening seconds immediately after the break, Harris' men really did a job on their opponents thereafter.
The work-rate was at times phenomenal as Millwall chased, harried and closed down Dale every time the visitors were in possession, whilst looking dangerous going forward.
A prime example was frontman Morison, who grabbed the third, killer goal on the hour-mark to crown a really industrious display. Onyedinma started the move and slipped the ball to O'Brien on the right, his slipped through pass split the visiting defence and Morison took two touches before lifting the ball over the keeper to find the back of the net with a composed finish.
Millwall by now had the bit between their teeth, and with the home fans really getting behind the team once again, this was a two-goal cushion that was not going to be relinquished.
It took a great double save by Lillis to deny The Lions a fourth goal, diving to parry Ed Upson's shot and then thwarting fellow sub Lee Martin with his fiercely struck follow-up shot at the near post.
Despite not grabbing a fourth goal to really put the icing on the cake, the players certainly gave everything that manager Harris and the supporters could have asked for as they recorded a fourth win in five games.
Millwall: Archer, Edwards, Craig, Beevers, Webster, Ferguson (L.Martin, 80mins), Williams, Abdou, Morison, O'Brien (Marquis, 76mins), Onyedinma (Upson, 61mins). Subs not used: Forde, J.Martin, Gregory, Thompson.
Booking: O'Brien (62mins)
Scorers: Abdou (4mins), Williams (44mins), Morison (60mins)
Rochdale: Lillis, McNulty, Lancashire, Vincenti, Lund, Allen, Rose (McDermott, 69mins), Cannon, Kennedy, Bunney (Andrew, 46mins), Henderson (Alessandra, 68mins). Subs not used: Diba Musangu, Rafferty, Eastham, Camps.
Bookings: Cannon (62mins), Vincenti (82mins)
Scorer: Vincenti (43mins)
Ref: J. Adcock
Att: 8,023 (away 383)