Manchester United twice came from behind to seal a thrilling 4-2 win over Aston Villa in the EFL Cup, avenging Sunday's Premier League defeat to Unai Emery's men.
With Erik ten Hag resting several key players and Cristiano Ronaldo absent through illness at Old Trafford, United fell behind through Ollie Watkins' well-taken finish at the start of a frantic second half, though Anthony Martial swiftly levelled.
United then went 2-1 down when Diogo Dalot put into his own net, but Marcus Rashford's strike set up a grandstand finish.
Fernandes saw an effort deflect off Tyrone Mings before nestling in the top-left corner and McTominay finished the visitors off to ensure United advanced to the fourth round following a back-and-forth encounter.
A much-changed United made a slow start and Villa went close when McTominay made a goal-line clearance from Douglas Luiz's in-swinging corner before the break.
The match burst into life three minutes after the restart, however, with Watkins racing onto Jacob Ramsey's pass to lift a neat finish beyond Martin Dubravka.
But United responded just a minute later, as Fernandes beat the offside trap before teeing up Martial to tap home.
The game's topsy-turvy nature continued when Dalot prodded into his own net from close range, but United found another leveller within five minutes as Rashford beat Mings before firing home.
With penalties in sight, Villa were the architects of their own downfall.
Substitute Alejandro Garnacho capitalised on a Robin Olsen error to feed Fernandes, who put the hosts ahead.
Garnacho was key again as United made the win safe, lifting a fine ball into the path of McTominay, who guided beyond Olsen in stoppage time.
What does it mean? United stay in trophy hunt
While qualification for the Champions League represents a key target for Ten Hag in his first campaign at Old Trafford, the Dutchman will also be expected to end United's trophy drought sooner or later.
United's last major trophy win came when Jose Mourinho oversaw a Europa League triumph in 2016-17, having also led them to the EFL Cup earlier that campaign.
The Red Devils approached Thursday's match looking to avoid suffering a third consecutive EFL Cup defeat for the first time since a run of five between 1979 and 1981, but their never-say-die attitude – as well as some poor Villa defending – helped them into the hat for the fourth-round draw.
Fernandes leads from the front
With United captain Harry Maguire struggling for game-time in the Premier League this season, Fernandes has often taken on the role of stand-in skipper since Ten Hag took the reins.
While Maguire's presence meant Fernandes was without the armband on Thursday, he still led from the front with a decisive contribution. The Portugal midfielder recorded a goal and an assist as he took centre stage during a frantic second half, while he also led his team-mates for expected goals (0.6 xG), shots (seven) and shots on target (four).
Garnacho makes his mark
United have high hopes for Garnacho, who fired Ten Hag's team to a Europa League win at Real Sociedad a week ago.
The 18-year-old showed his quality during an impressive cameo against Villa, laying on two assists following his 62nd-minute introduction.
United go to Fulham for their final Premier League game before the World Cup on Sunday, while Villa visit Brighton and Hove Albion on the same day.