Steve Cooper was determined to make home advantage count for the four-time winners yet Marcus Rashford quickly silenced the Forest faithful with a blistering run and finish in only the sixth minute.
A brief response midway through the half brought the locals back into play before Wout Weghorst’s scored a timely first goal for the club on the verge of half time. Bruno Fernandes made the game safe late on.
United had started by far the better team and yet lacked the end product to back up their zippy play, Antony firing wide with two tame efforts after Rashford’s opener.
In fact, it was from the goalscorer’s giveaway that Forest first threatened. Morgan Gibbs-White played a fine ball in behind for Sam Surridge to fire home against the run of play. However, VAR brought the move back for a narrow offside.
Gustavo Scarpa and Brennan Johnson threatened for the hosts, now finally an active participant in the tie, the latter forcing David De Gea into a low save before a delightful run beat two challenges and shot over the bar.
United looked to be heading into the break on the back foot, Erik ten Hag furious at Fernandes hashing a long-range shot well wide of goal. And yet, within moments, they scored again.
Antony’s volley from 18 yards was parried by Wayne Hennessey straight to Weghorst, who successfully maneuvered an unorthodox finish into the roof of the net just as the clock hit 45 minutes.
With one foot in Wembley after only a quarter of the tie, United faced few difficult questions after emerging for the second half. Christian Eriksen curled an effort onto the crossbar after 54 minutes.
Shortly afterwards, Rashford went down clutching his ribs and was quickly withdrawn after getting clipped, although he walked off fairly comfortably with his job done for the night by the hour mark.
Ten Hag opted for pace off the bench with Alejandro Garnacho, Anthony Elanga and Facundo Pellistri entering the fray. It was the Uruguayan who caused issues as the ball broke in the 88th minute for Fernandes to slam home a volley from 20 yards and surely book a spot in the final.
Forest will attempt to revive their bid to reach Wembley with the second leg at Old Trafford next Wednesday.