McCarthy earned his first win as boss in his third match last weekend at Bristol City, and his side made it two on the bounce on a snowy night in South Yorkshire.
They were under pressure for most of the first half but Rotherham couldn’t convert their dominance, and Sheyi Ojo grabbed the lead on the counter just before the break.
Matt Crooks tapped in a leveller but, as the weather brought deteriorating pitch conditions, the final piece of quality saw Bennett head in a Josh Murphy cross five minutes from time.
Story of the match
Rotherham were seeking a third consecutive win and started impressively, dominating much of the first half. After Ben Wiles and Michael Smith had early efforts blocked, another strike from Smith flew inches wide of the far post after taking a slight deflection.
Smith would work the goalkeeper the next time in a similar situation. His partnership with Matt Crooks has flourished since the turn of the year and the support striker showed nice feet before playing in Smith, whose early strike forced Dillon Phillips, deputising for the ill Alex Smithies, into a good low save.
Rotherham were hitting their stride and playing some great football, none more so than in one sweeping move that started with goalkeeper Viktor Johansson, involved a brilliant Crooks ball for Wiles, whose cross for Matt Olosunde led to a blocked shot and Lewis Wing mishit.
The pressure kept coming, and Phillips made an exceptional save to tip a Smith header, from Wing’s cross, over the bar from just a few yards out. Michael Ihiekwe then found the side netting and it looked like only one team could possibly open the scoring.
But Cardiff staged a rally of sorts, and after Keiffer Moore sent a warning shot from distance which forced a first Johansson save, Harry Wilson’s pass caught the home side out at the back on the counter and Ojo sprinted in to beat the keeper one-on-one and steal a half-time lead.
After that smash-and-grab, Cardiff came out a more confident side for the second half. Johansson made a phenomenal save to match Phillips’ in the first period, just doing enough to tip a Sean Morrison volley over his crossbar, before the keeper was relieved to see Moore head straight into his arms at point-blank range from a Will Vaulks cross.
Just as it seemed Cardiff had settled into the match at last, Rotherham hit back as the duo of Crooks and Smith made their mark once again. Even when more than 30 yards apart there seems a telepathic connection, and from the sideline Smith managed to pick out his partner at the back post with a delightful cross along the ground that evaded everybody to gift Crooks a tap-in.
The visitors pushed unperturbed by the setback and substitute Murphy had a great chance, lifted over Johansson but over the crossbar as well, before the snow - which had incidentally caused the postponement of this fixture last month - began to really fall, bringing a delay to retrieve a batch of yellow balls and, more seriously, a challenging surface.
Neither side could find a rhythm but one moment of quality would be enough, and that was provided just in time by Cardiff. Murphy whipped in an excellent cross from the right and wing-back Bennett was unmarked at the back post to steer in the winning goal.
There was still time for late drama in added time, as referee Geoff Eltringham - who waved away protest after a push on Smith in the first half - denied Rotherham a penalty again when a cross appeared to strike the hand of their former player Vaulks, before Wing blasted over the final kick of the match.
Man of the match: Sheyi Ojo (Cardiff)
The most threatening forward player for Cardiff and calmly in a second goal in four under McCarthy before the break.