Roberto Firmino and Sadio Mane scored in the first half before Mohamed Salah and Daniel Sturridge wrapped a deserving thrashing for Arsene Wenger's side.
Meanwhile, Tottenham remain winless at Wembley. Dele Alli's close-range finish looked to see off Burnley until debutant Chris Wood finished off a counter-attack in the 92nd minute.
Earlier in the day, Alvaro Morata impressed as Chelsea continued to climb the Premier League table with a 2-0 win against Everton at Stamford Bridge.
EPL Table | Premier League 2017-18 season table
| Pos | Team | P | W | D | L | GD | Pts |
| 1 | Man Utd | 3 | 3 | 0 | 0 | 10 | 9 |
| 2 | Liverpool | 3 | 2 | 1 | 0 | 5 | 7 |
| 3 | Huddersfield | 3 | 2 | 1 | 0 | 4 | 7 |
| 4 | Man City | 3 | 2 | 1 | 0 | 3 | 7 |
| 5 | West Brom | 3 | 2 | 1 | 0 | 2 | 7 |
| 6 | Chelsea | 3 | 2 | 0 | 1 | 2 | 6 |
| 7 | Watford | 3 | 1 | 2 | 0 | 2 | 5 |
| 8 | Southampton | 3 | 1 | 2 | 0 | 1 | 5 |
| 9 | Tottenham | 3 | 1 | 1 | 1 | 1 | 4 |
| 10 | Burnley | 3 | 1 | 1 | 1 | 0 | 4 |
| 11 | Stoke | 3 | 1 | 1 | 1 | 0 | 4 |
| 12 | Everton | 3 | 1 | 1 | 1 | -1 | 4 |
| 13 | Swansea | 3 | 1 | 1 | 1 | -2 | 4 |
| 14 | Newcastle | 3 | 1 | 0 | 2 | 0 | 3 |
| 15 | Leicester City | 3 | 1 | 0 | 2 | -1 | 3 |
| 16 | Arsenal | 3 | 1 | 0 | 2 | -4 | 3 |
| 17 | Brighton | 3 | 0 | 1 | 2 | -4 | 1 |
| 18 | Bournemouth | 3 | 0 | 0 | 3 | -4 | 0 |
| 19 | Crystal Palace | 3 | 0 | 0 | 3 | -6 | 0 |
| 20 | West Ham | 3 | 0 | 0 | 3 | -8 | 0 |
Morata set up Cesc Fabregas for the opening goal in Sunday's west London clash, and then made the game safe for Antonio Conte's champions with a powerful header.
Earlier on in gameweek 3, Marcus Rashford came off the bench to score as Manchester United extended their perfect start to the season with a 2-0 win over Leicester City on Saturday.
Manchester City temporarily led the top flight after a dramatic late 2-1 win at Bournemouth. Eddie Howe's Cherries impressed early on at Dean Court, and Charlie Daniels deservedly put the hosts ahead 13 minutes in with a stunning half-volley from wide on the left into Ederson's top left-hand corner.
In Pictures | Chelsea vs Everton | 27/08/2017
Bournemouth's lead didn't last long though, as David Silva - excelling in the No.10 role with Kevin de Bruyne playing deeper - slipped in Gabriel Jesus for a neat finish eight minutes after Daniels' rocket.
Both sides went close to a winner after the break as Josh King and Nicolas Otamendi hit the woodwork at either end, but Pep Guardiola's side won it at the death as Raheem Sterling scored in the sixth minute of injury time.
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Crystal Palace and West Ham remain rooted to the bottom of the table after defeats to Swansea (2-0) and Newcastle (3-0) respectively.
