MARCUS Rashford failed to score for the first time in 10 Old Trafford appearances but Manchester United could rely on some Brazilian magic to ease into the FA Cup fifth round.
Casemiro scored two stunning goals, inside four minutes early in the second half, and Fred was on the mark also as the Reds march on on four trophy fronts under Erik ten Hag.
United enjoyed the best of the first-half chances, and Rashford saw a goal ruled out for a Wout Weghorst offside on 34 minutes.
But the tie changed on 54 minutes, although it was Casemiro, with his third goal for the club, rather than Rashford, who broke the deadlock and put his team on course for a 14th win in their last 17 games.
Christian Eriksen sparked the move with a characteristic sweeping pass out to the left where Antony cut in and played a quick, telling pass inside two Reading defenders for Casemiro to chase through and lift a perfect finish over the advancing keeper.
Even more remarkable was to follow four minutes later, as Casemiro scored his, and United’s second, in stunning fashion as Reading, for one of the few times on the evening, lost their shape and discipline.
United had the time and space to work the ball inside, with Fernandes finding Fred whose short pass moved the ball back to Casemiro.
With no defenders in sight, the Brazilian had time to curl a shot from fully 30 yards which moved so late and dramatically that the keeper, and crowd, appeared to think it had first passed wide of the goal.
Any suggestion of a Reading recovery - and there had not really been one - was removed on 64 minutes when Andy Carroll, booked four minutes earlier for a rash challenge on Malacia, was shown a second yellow, and sent off, for an even more stupid foul on Casemiro.
But, having waited so long for an opening goal, a couple more - one at each end - followed in quick succession first when Bruno Fernandes’s right-wing cross was turned in cleverly by substitute Fred at the near-post with a neat back-heel on 66 minutes.
Just six minutes later, and hugely against the run of play, a Tom Ince corner found United’s defence lacking as substitute Amnadou Mbengue leaped impressively to head in from six yards.
As ten Hag, who expects to reach the EFL Cup Final on Wednesday when they play the second leg of a semi-final with Nottingham Forest that they lead 3-0, ran his bench, there were still plenty of chances.
Young substitute Facundo Pellistri came closest to adding a fourth but was unable to scramble in a cross from fellow replacement Alejandro Garnacho at the far post.
De Gea 6 - Wan-Bissaka 7, Lindelof 7, Maguire 7, Malacia 5 - Casemiro 9 (Mainoo 73, 5), Eriksen 7 (Fred 57, 8) - Antony 6, Fernandes 7 (Pellistri 68, 6), Rashford 7 (Garnacho 68, 6) - Weghorst 7 (Elanga 72, 5).
Subs not used: Martinez, Varane, Heaton, Williams.
Lumley 5 (Bouzanis 75, 5) - Hoilett 5 (Mbengue 69, 7), Yiadom 5, Holmes 6, McIntyre 5, Rahman 5 - Hendrick 5 (Craig 75, 5), Loum 5 (Fornah 61, 5), Ince 6; Lucas Joao 6 (Long 76, 5), Carroll 4.
Subs not used: Dann, Meite, Azeez, Guinness-Walker.