Erling Haaland scored a hat-trick as Manchester City maintained their perfect Premier League start with a 5-1 thrashing of Fulham on Saturday, as Son Heung-min's also netted three times in Tottenham's 5-2 victory at Burnley.

But Chelsea's huge investment in the transfer market is still to reap reward as the Blues were beaten 1-0 at home by Nottingham Forest.

In keeping with the early weeks of the season, City were good enough for the three points without ever hitting top gear.

The English champions were without manager Pep Guardiola as he recovers from back surgery in his native Catalonia.

The home side had not had a shot on target until Julian Alvarez turned home Haaland's cross to open the scoring on 31 minutes.

Fulham, who were missing influential midfielder Joao Palhinha after his deadline day move to Bayern Munich collapsed on Friday, responded immediately when Tim Ream tapped in from a corner.

City needed a set-piece of their own to restore the lead in controversial circumstances.

Nathan Ake's header was allowed to stand despite Manuel Akanji, who was in an offside position, jumping over the ball.

Haaland then exploded after the break. He became the fastest player to reach 40 Premier League goals, in just 39 appearances, with a cool finish from Phil Foden's through ball.

The Norwegian then put his missed penalty at Sheffield United last weekend behind him to slot home from the spot.

And he made it six goals in five games this season by completing his hat-trick in stoppage time.

Spurs sit just two points behind City as their sparkling start under Ange Postecoglou continued.

Burnley had taken the lead after just four minutes at Turf Moor through Lyle Foster.

But Son, who was moved into a more central role by Postecoglou in place of Richarlison, soon proved his manager had pulled off another masterstroke.

The Tottenham captain's deft chip levelled before a thunderous strike from Cristian Romero put the visitors in front in first-half stoppage time.

James Maddison's curling finish from the edge of the box made it 3-1 before Son took centre stage to score twice in three minutes to complete his hat-trick.

Chelsea's spending on deadline day took their total splashed on new players in just over a year under a consortium fronted by Todd Boehly to over £1 billion (US$1.3 billion).

Moises Caicedo's move from Brighton that could rise to £115 million broke the British transfer record last month.

But the Ecuador international was at fault for the only goal at Stamford Bridge to leave Mauricio Pochettino's men embarrassed.

Anthony Elanga slotted home three minutes into the second-half after Caicedo gave the ball away inisde his own half.

New signing Cole Palmer was thrown on to try and turn the game around, but Chelsea's lack of a natural goalscorer, despite their huge outlay, was again exposed.

Pochettino has won just one of his first four games in charge to leave Chelsea already eight points adrift of City.

Bournemouth were denied their first win under Andoni Iraola as Bryan Mbuemo snatched a 2-2 draw for Brentford.

Sheffield United and Everton secured their first point of the season after a pulsating 2-2 draw in the lunchtime kick-off.

Cameron Archer's debut strike and a Jordan Pickford own goal put the Blades in front after Abdoulaye Doucoure's early opener for Everton.

Arnaut Danjuma levelled early in the second-half, but Everton needed some heroics from Pickford in stoppage time to prevent slipping to a fourth straight defeat.

And in the late game, Newcastle lost their third game on the trot after 18-year-old Evan Ferguson's hat-trick gave Brighton an impressive 3-1 win at the Amex. (AFP)