After a first half during which Reading, 14th in the Championship, frustrated Erik ten Hag's team, the Brazilian midfielder scored twice in four minutes after the break. Fred came off the bench to score a third with a clever flick after Reading striker Andy Carroll had been sent off for picking up two yellow cards.
Amadou Mbengue's score gave the travelling fans something to cheer with a consolation goal but it's United who are into the draw with the next round.
1. Casemiro is key for Ten Hag
Had the summer gone differently, Frenkie de Jong might have been wearing United's No. 18 shirt against Reading and Casemiro could have still been at Real Madrid. Ten Hag, however, will be happy that it worked out the way it did.
The Brazilian midfielder turned the tie against Reading with two quick goals in the second half -- the first with a clever finish from Antony's pass and the second with a shot whipped into the corner from outside the box.
Casemiro has only been at Old Trafford for a matter of months but there's already an argument that he's United's most important player. No one else is the squad can do what he does and it has reached the point where he's almost irreplaceable. Of the 21 games he has started since arriving from Madrid, United have lost only two, and it was glaringly obvious how big a miss he was during the 3-2 defeat at Arsenal.
A place in the top four and a trophy would be a monumental success for Ten Hag in his first season, but he needs Casemiro -- above anyone else -- to stay fit. After Fred scored the third goal against Reading, Casemiro was quickly substituted to save his legs.
2. Man United progress but squad is getting stretched
Ten Hag is leaving the door open for more signings before the Tuesday transfer deadline but it's likely this will be his squad between now and the end of the season and it's already looking stretched. The Dutchman picked a strong team against Reading -- probably stronger than many expected given the opposition were a mid-table Championship side -- but a number of absences meant there were five youngsters on the bench.
With Anthony Martial, Scott McTominay, Diogo Dalot, Luke Shaw and Jadon Sancho all missing the squad begins to look thin, which is an issue when United are the only English club left in four competitions. It's a sign of the progress made under Ten Hag that they're winning games and progressing in competitions but it's debatable whether he has the resources to cope with such a congested fixture list.
United have eight games in February, starting Wednesday with the Carabao Cup semifinal second leg against Nottingham Forest. The FA Cup fifth round is pencilled in for March 1, but before then Ten Hag has to deal with five Premier League games, a two-legged Europa League tie against Barcelona and, potentially, the Carabao Cup final. It's a mammoth task when injuries are starting to pile up.
3. Reading miss out in key moments
Reading manager Paul Ince, once of United's midfield, will not have arrived at Old Trafford expecting to leave with very much but he might look back on a couple of moments and think that the outcome could have been different.
His team defended well for much of the first half and just before the break, David de Gea needed to be alert to block an effort from Junior Hoilett. It really needed to go in to give Reading any chance of getting a result.
Carroll's ridiculous red card when the score was already 2-0 gave the visitors a mountain to climb but when Mbengue scored from a set piece to make it 3-1, Reading were on top and Ince was left furious on the touchline when a quick counterattack, which should have ended in another goal, fizzled out.
You have to take your chances if you want to cause a cup upset and Reading didn't take advantage of theirs. On another day, it might have been a more nervous game for United.
Best and worst performers
Casemiro, MF, Manchester United: He's not on the team to score goals but two in four minutes won the tie against Reading after a tight first half.
Antony, FW, Manchester United: The Brazilian has taken some criticism for being too predictable since his summer move from Ajax but it was his wonderful pass that created the first goal for Casemiro.
Tom Holmes, DF, Reading: Defended well, particularly in the first half, throwing himself in front of everything as United looked for the opening goal.
Andy Carroll, FW, Reading: The veteran striker charged around for most of the game looking like he was desperate to get sent off and referee Darren England finally gave him a second yellow card for a late challenge on Casemiro.
Tyrell Malacia, DF, Man United: The young full-back was bailed out with De Gea when his mistake gifted a chance to Hoilett with the score at 0-0.
Tom Ince, MF, Reading: The son of manager Paul was once tipped for the top but he had little impact on the game.
Highlights and notable moments
Is there a better defensive midfielder in the world right now? With Casemiro commanding the pitch and scoring twice (including this deflected shot from distance), hard to argue for anyone else.
CASEMIRO FROM DISTANCE FOR HIS SECOND GOAL 😱 pic.twitter.com/O5nLQD9Ml1— ESPN FC (@ESPNFC) January 28, 2023
United's third on the night was a cheeky flick and finish from Fred.
THIS FINISH FROM FRED ⚡ pic.twitter.com/CajEFA4cXu— ESPN FC (@ESPNFC) January 28, 2023
Not sure if was meant to be a back-heel pass into the box, but the Old Trafford faithful will take it.
After the match: What the players/managers said
Manchester United captain Harry Maguire, on Casemiro: "He's done what he was brought in to do, He's a phenomenal player. You don't win what he's won without being a top player ... He's improved the team, the morale and the performance."
Manchester United manager Erik ten Hag on Casemiro: "We know he's a great player. In [Real] Madrid's midfield with [Toni] Kroos and [Luka] Modric it was great. I think he's capable, you see offensively he has a part and he enjoys it. What I like is dynamic football with variations, many position switches."
Key stats (provided by ESPN Stats & Information research)
- Casemiro couldn't complete the hat trick, which would have been the first of his career. The last Manchester United player to score three in a match is still Cristiano Ronaldo (April 2022 vs. Norwich).
- Marcus Rashford couldn't become the first player in Manchester United history to score in 10 straight matches. The VAR decision to overrule his would-be goal in the first half is the third such against United this season in all competitions. The only Premier League team with more is Nottingham Forest (4).
Manchester United: A slew of games across all sorts of competitions will make for a busy February. They host Nottingham Forest in the second leg of the Carabao Cup semifinals next Wednesday, holding a one-goal advantage. Then three Premier Leagues games (Crystal Palace, Leeds United twice) across eight days. And then? A trip to Barcelona on Feb. 16 in the first leg of the Europa League knockout round.
Reading: With their FA Cup run now complete, back to trying to move up the Championship table. They host Watford Feb. 4.