Solskjaer thrilled as United make it look easy
Arsenal 1 Manchester Utd 3
Alexis Sanchez scored on his return to the Emirates Stadium as Manchester United saw off Arsenal to reach the fifth round of the FA Cup and extend Ole Gunnar Solskjaer's winning start.
The two most successful sides in the competition's history played out an entertaining game last night as United secured a 3-1 win and an eighth straight victory for interim manger Solskjaer.
Sanchez and Jesse Lingard had set the visitors on course for victory before Pierre-Emerick Aubameyang pulled a goal back for the Gunners, only for substitute Anthony Martial to wrap up a comfortable win with a late strike.
Solskjaer retained his perfect record in charge of the Red Devils after making five changes - including starts for fit-again Sanchez and striker Romelu Lukaku.
Meanwhile, the defeat could have further-reaching consequences for Arsenal, who lost central defensive pair Sokratis Papastathopoulos and Laurent Koscielny to injuries as Mesut Ozil came off the bench for his first appearance since Boxing Day.
Thrilled boss Solskjaer said: "It's fantastic to go through in the cup. It's one of the hardest games you can get.
"I've had a [selection] headache since I came because the squad is full of good players. It's up to us to pick the right tactics and players. We need to rest a few as there's big games coming up. But we have fresh legs.
"Today we looked more like a proper team. We looked more structured. We'd worked hard at defending and counter-attacking. Counter-attacking is classic Manchester United - Wayne Rooney, Cristiano Ronaldo, Ji Sung-park - we've scored so many at Arsenal over the years.
"Today was a big step forward. It was a massive improvement from the Tottenham game. It's easy to get excited and talk about the future but we need to just keep working and think about the next game.
"Towards the end it was comfortable but not during the 90 minutes."
Lukaku, who claimed two assists, said: "We had clear direction today and I'm really happy with the win and the manner in which we played.
"I just take it a day at a time. I work hard in training and it paid off today and we own.
"Now it's up to me to keep working and help the team with goals and assists.
The guys just have to put the ball in the back of the net! I always wanted to be a player who can do both, score goals and get assists.
"Look at the history of the club, we make a statement wherever we go. We look to dominate and create as many chances as we can."
Arsenal boss Unai Emery revealed that Laurent Koscielny went to hospital and "maybe" has a broken jaw.
Sokratis also limped off with what appeared to be a twisted ankle.
Emery said: "Our injuries changed the possibility to do something different on the pitch. They have been clinical over the 90 minutes. We had chances but couldn't score and that's the difference.
"I hope they are not two big injuries. Our game-plan worked well, we had pressure and chances but in the second half we can take some risk.
"The players worked well to win this match but we lost today. We deserved more.
"I think we worked well. Our injuries changed our possibility to do something different."
He added: "When we were 2-1 down we had chances to draw but we didn't score.
"Sokratis hurt his ankle - I hope not a lot. Koscielny is different. It was maybe a break. I hope not but he's going to hospital and we're going to wait.
"We played a team in a good moment. We lost this match but I'm happy with our work. The supporters helped us.
"We need to think about the Premier League. We won against Chelsea and are close. We need to push in that competition and we have another important competition in the Europa League."
Petr Cech, making his first start since announcing his retirement at the end of the season, was quick off his line to deny Paul Pogba after he was played in by Sanchez early on.
Sanchez, who was roundly jeered by the home fans who have still not forgiven the 30-year-old for leaving for United last January in exchange for Henrikh Mkhitaryan, would be the man to open the scoring.
Ander Herrera played in Lukaku, whose slide-rule pass set Sanchez through on goal, with the Chilean showing composure to round Cech and finish from a tight angle.
Just two minutes later and the lead was doubled, Herrera and Lukaku again involved as United were allowed to break unchallenged, with Lingard coolly side-footing home another pass from the Belgium striker.
Arsenal responded and pulled a goal back before half-time, Aubameyang tapping home at the back post after an Alexandre Lacazette touch diverted Aaron Ramsey's low cross into his path.
Arsenal were straight out of the traps after the interval as Ramsey's close-range header was tipped onto the crossbar and behind by Romero.
With the hosts chasing the tie, they suffered another setback as captain Koscielny was forced off after suffering a gash to the face from a stray Lukaku boot.
United were playing on the counter-attack, and Solskjaer opted to introduce both Marcus Rashford and Martial for the final stages.
Lacazette stung the palms of Romero with a driven strike but Unai Emery's side were soon caught out with men committed upfield.
United broke and Pogba's shot was pushed into Martial's path by Cech - with the France forward making no mistake in securing his side's place in Monday's draw.
A late flashpoint saw Sead Kolasinac and Rashford escape with bookings after VAR aided Craig Pawson identify the main culprits - but both players could have been sent off for butting heads.