The demolition followed a moment of madness on 40 minutes with Cameroon trailing to Ivica Olic's early far-post finish.
Song lashed out at Mandzukic in an innocuous off-the-ball incident in midfield and was rightly given his marching orders.
The indomitable Lions were missing the leadership of Samuel Eto'o and lacked a clinical presence in the penalty area but almost snared a consolation in the dying seconds when Pierre Webo hit the crossbar with a header.
Cameroon's frustration was all too evident when full-back Benoit Assou Ekotto and team-mate Benjamin Moukandjo had to be separated after butting heads in the closing stages. The Tottenham owned defender, who spent last season on loan with QPR, stalked down the tunnel at full-time, despite efforts by Eto'o to calm him down.
The victory means Croatia keep their hopes of reaching the last 16 alive ahead of another winner takes all showdown with Mexico in their final group match on Monday.
PRE-MATCH: One top striker in, one out: Croatia welcome back Mario Mandzukic from suspension while Cameroon leave Samuel Eto'o (knee) on the bench.
11' - GOAL! CROATIA 1-0 CAMEROON. Ivica Olic arrives at the far post to gleefully fire home after sensational vision from Perisic. Srna crossed towards Mandzukic from the right and when the ball fell to Perisic he showed magnificent awareness to pick out Olic.
17' - CROATIA CHANCE! The corner falls for Mandzukic, who knocks down for Perisic but he somehow fails to convert from four yards out. Good save by Itandje, but he should score. Let off for Cameroon.
40' - SONG RED CARD! Sheer madness from the Barcelona man as he elbows Mandzukic in the back for no apparent reason.
48' - GOAL ! CROATIA 2-0 CAMEROON. Cameroon are going out. Perisic latches onto a woeful kick by Itandje and surges into the area from the left before flashing a shot inside the near post. It's 2-0 and game over.
51' - WHAT A MISS! It's the parting of the waves as Mandzukic is sent racing through the middle. He's clear on goal but somehow contrives to stick his effort wide of the post.
52' - CAMEROON CHANCE! A high cross from the left drops to Nounkeu at the far post who flashes a volley over the bar. Decent effort.
61' - GOAL! CROATIA 3-0 CAMEROON. It's three. Mandzukic marks his return from suspension with a bullet header from a left-wing corner. It was trademark stuff from the Bayern hitman, but Cameroon's marking was poor.
73' - GOAL! CROATIA 4-0 CAMEROON. Mandzukic makes it four with a simple tap-in after Itandje spilled a low shot from the right by Eduardo.
88' - CROATIA CHANCE! Cameroon still pushing for that goal... but it's leaving gaps at the back. Rebic plays in Rakitic in the area, who dinks it past Itandje but can't get to the ball to put it in from a tight angle.
89' - OFF THE BAR! Webo crashes a header into the ground and onto the bar from Assou-Ekotto's left-wing cross.
4393 - The number of days between Ivica Olic's 1st goal at the World Cup (June 2002) and his second one tonight.
Croatia have scored in three successive World Cup games for the first time since their run to third place in 1998.
Olic is now Croatia's oldest goalscorer in World Cup history.
Croatia have scored 3+ goals in a World Cup game for the first time since the 1998 quarter-final versus Germany.
The Croats have scored as many goals against Cameroon (four) today as they have in their last seven World Cup finals matches combined.
Mario Mandzukic has scored 15 goals for club and country in his last 27 apps.
Ivan Perisic is the sixth player in this World Cup to register both a goal and assist in a single match.
Cameroon are the first team to lose six successive World Cup games since El Salvador in 1982
Croatia scored four times in a World Cup game for the very first time.
Mario Mandzukic is the first player to score two goals in one World Cup match for Croatia
The Song family (Rigobert and Alex) have picked up three of Cameroon's eight red cards at the World Cup.
Since their first World Cup qualification in 1982, no country has received more red cards than Cameroon (8, joint with Argentina).
(Stats courtesy of Opta)
With Mandzukic back, how far can Croatia go in this tournament? Niko Kovac's side still face a tough task to see off Mexico to make the last 16, but with their leading marksman back with a bang, you wouldn't rule them out. A solid back four and a midfield full of artistry means they will be a match for anyone on their day and on this evidence they would be a team to avoid in the knockout stages.
MAN OF THE MATCH
Mario Mandzukic (Croatia): Ivan Perisic ran him close with a magical display but the two-goal hitman just shades it for his clinical finishing and all-round forward play. He is key to Croatia's hopes of going far in this competition.
Croatia: Pletikosa 7, Pranjic 7, Perisic 8, Corluka 7, Lovren 7, Rakitic 8, Modric 8, Srna 7, Mandzukic 8, Olic 7, Sammir 6. Subs: Eduardo 7, Kovacic 7, Rebic 7.
Cameroon: Itandje 5, Assou-Ekotto 6, Nkoulou 6, Song 3, Choupo Moting 5, Chedjou 5 , Mbia 5, Enoh 5, Matip 6, Moukandjo 6, Aboubakar 6. Subs: Nounkeu 6, Webo 7, Salli 6.
THE MATCH IN A TWEET
- Sports & Recreation
- Mario Mandzukic
- Ivan Perisic
- Ivica Olic
- Ivan Rakitic