Further goals from Jesse Lingard and Anthony Martial, either side of a Pierre-Emerick Aubameyang effort for Arsenal, sent United through to the fifth round and made it eight wins from eight under the Norwegian's interim spell.

Solskjaer knows that Sanchez has more to give and hopes his goal can help him kick on.

"It wasn't like Alexis had an open goal, it was a great finish," he said of the 31st-minute opener.

"Every player, the more confident you get the more you want to get on the pitch and train and work on yourself and you trust yourself.

"He has been injured lately so it was great to see him get 65-70 minutes tonight and he can only improve and I think he knows that himself."

It was a dominant display by United, far more controlled than that of their 1-0 win in the other half of north London at Tottenham a fortnight ago.

Solskjaer was pleased with how his side stepped up their performance and reckons it was the one of the best of his eight-game winning stint.

"It was a massive step forward for us performance wise, as a team, the structure in the team was miles, miles, miles better compared to Tottenham a couple of weeks ago where we hung in there and David (De Gea) saved us," he added.

"Today, Sergio (Romero) had a fantastic save at the start of the first half, but our structure was miles, miles, miles better.

"We have been working on that, we need to dig in and defend properly against good teams.

"I am not here to get excited, I am here to keep on improving the team, improving the players and just look to the next game.

"It is a league game, a massive league game for us at home again. Tomorrow we will enjoy sitting back in the chair and enjoy watching the FA Cup."

The foundations of the win were laid with two goals in two first-half minutes as Sanchez's smart finish was followed soon after by a composed Lingard finish, with the visitors picking large holes in the home defence.

Aubameyang's 17th of the season made a game of it before the half-time but Martial's goal late on sealed the victory.

Arsenal's chances were hampered by injuries to defenders Sokratis Papastathopoulos and Laurent Koscielny, who has gone to hospital with a possible broken jaw.

"I think they weren't big injuries for Sokratis," boss Unai Emery said. "Maybe Laurent Koscielny is going to hospital to [analyse] what injury he has. Maybe he's broken his jaw but I hope not.

"I'm happy because I think our work is good, but the result is bad. Today it's the result and the injuries.

"They don't help us to be in the match, maybe when the result's 1-2. In this moment we had the possibility to grow and to win, but these injuries – especially the one to Koscielny – didn't help us because our rhythm went down.

"Also, we needed to change different players to play at centre-back.

"They were very clinical today and in the moments when we attacked, we got into the box but couldn't produce the last action to score.

"We deserved more but we played against Manchester United who are in their best moment of the season, and they have a lot of players to make the difference. (Marcus) Rashford and Martial came on as well."

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