Those goals came inside the opening 60 minutes, with Fabio Vieira and Takehiro Tomiyasu adding two more late on.
The win means Arsenal are now second in the Premier League and two points off leaders Tottenham.
Simon Collings was at Emirates Stadium to see Arsenal in action...
David Raya 6
Did not have much to do, but looked much more assured than in recent weeks. Distribution was good - picked out Gabriel Martinelli a few times on the counter.
Ben White 7
Another good game from the right-back, who went close to scoring in the second-half. Taken off and rested with 25 minutes to go.
William Saliba 7
Didn't give Sheffield United striker Rhian Brewster a sniff all afternoon. So dominant and composed on the ball.
Jakub Kiwior 7
A surprise starter at centre-back but he had a good game. Has improved a lot in possession this season.
Oleksandr Zinchenko 7
Brought into the team as Arsenal were due to dominate the ball. Saw plenty of it and didn't ever give it away.
Kai Havertz 6
Rotated quite a lot with Saka during the first half and so cropped up on the right wing. Not the big performance fans are waiting for, but solid.
Setup the opening goal with a great pass to Nketiah. Another flawless display at the base of midfield. Did not put a foot wrong.
Emile Smith Rowe 6
Made his first Premier League start in over 500 days. Starting to look closer to his usual self. Setup Nketiah's third goal.
Bukayo Saka 6
Captained the side from the start for the first time in his career. Made a few bright runs and his corner was fired home by Nketiah for Arsenal's second.
Eddie Nketiah 9 | Star player
Opened the scoring with a well-taken goal in the first-half. Grabbed a second after the break with a classic poacher's finish from a corner and then lashed in a third for his hat-trick. Brilliant performance.
Gabriel Martinelli 6
Had some lively moments in the first-half, especially when Arsenal could hit Sheffield United on the counter.
Takehiro Tomiyasu (White 65') 7
On at right-back with Arsenal 3-0 up and scored the fifth in injury-time, his first goal for the club.
Leandro Trossard (Martinelli 66') 6
On for Martinelli and tried to get at Jayden Bogle, who got booked.
Reiss Nelson (Saka 73') 5
Full of running as ever and pressed well.
Fabio Vieira (Vieira 73') 6
Won and scored a penalty to make it 4-0.
Mohamed Elneny (Rice 89') N/A
Subs not used: Ramsdale, Gabriel, Jorginho, Odegaard.