An injury-hit Manchester United had little choice but to field a near-full-strength XI for their trip to the East Midlands.
But it was a man making his first start since early January, Scott McTominay, who almost made a telling early contribution, when his header forced a simple save out of Matt Turner, shortly after Antony had rattled the crossbar.
The opening 20 minutes were breathless at times, and although it took Forest a little longer to settle, they eventually forced a smart stop out of André Onana when Taiwo Awoniyi’s wicked drive was beaten away by the Cameroonian.
Such was the changeable pattern of the first half, it soon swung back in United’s favour.
McTominay was again at the heart of the goalmouth action, with his header this time forcing a better save out of Turner, who turned his near post header away for a corner to keep the scoresheet unmarked going into the interval.
It was similarly frenetic after the break too, but it was the Tricky Trees who started brighter this time around, but in another duel between Onana and Awoniyi, the United stopper came out on top.
Onana was proving an immovable object in the United goal, as he was again on hand to deny Divock Origi shortly after, leaving Forest wondering just what they had to do to break the deadlock.
In truth, both sides were probably thinking the same, with a lack of quality in the final third hinting that this game was going to need extra-time to find a winner.
That was until Casemiro took matters into his own hands, stooping low at the near post to turn home a Bruno Fernandes free-kick in front of the travelling contingent.
It was a very timely winner for United, who certainly won’t have wanted extra-time with a Manchester derby to come against City on Sunday.
The victory sets up a blockbuster quarter-final tie against Liverpool at Old Trafford, and as painstaking as this defeat must feel for Forest, it is perhaps a blessing in disguise.
They can now focus solely on their battle to beat the drop in the Premier League, which resumes with the visit of Liverpool on Saturday.
Flashscore Man of the Match: Casemiro (Manchester United)
