The Norwegian phenomenon completed his treble in the space of just 26 minutes, with Joao Cancelo and Julian Alvarez (2) on target after the break.
It’s been a wonderful start to the season by the champions.
City, given space and time on the ball are as devastating as any team in the world – maybe the most devastating.
It is to Nottingham Forest boss Steve Cooper’s credit that he came to the Etihad to play football, but that should also come with a government health warning.
The arrival of Haaland has changed how City attack and, just five games in, it seems the who team are looking to find him whenever the goal is in sight.
It is a new and devastating dimension to our play, and it is threatening to wreak havoc to opposition defences up and down the land.
It’s hard not to get carried away, but when you No.9 has scores six goals in roughly 66 of open play over two matches.
The lethal Norwegian was at it again against Forest – one of his dad’s former clubs – with a first-half hat-trick completed in the space of 26 minutes.
The first came on 12 minutes after a Phil Foden cross floated towards the near post was poached by Haaland who got there a millisecond before the defender’s attempted clearance.
The second, 11 minutes later, was again created by Foden who burst into the box before squaring for Haaland to tap home.
The third was a close range header after John Stones had strained his neck muscles to nod the ball back across the box.
There was time for the lively Alvarez to strike the foot of the post with a low drive as the Blues looked to finish the game as a contest before the break.
The second-half saw City continue the rout.
Five minutes after the restart, Joao Cancelo joined the party, collecting Bernardo’s clever pass to whip home a sumptuous 20-yard shot into the top left corner.
Number five of the evening came on 65 minutes, with sub Riyad Mahrez’s clever flick sending Alvarez clear in the box and the Argentine’s low shot beat Dean Henderson to cap an impressive full Premier League debut with his first goal.
And it got even better for Alvarez as he finished emphatically from 10-yards after collecting Mahrez's deflected shot and firing into the top left corner three minutes from time.
Superb stuff all round.
How many might Erling get?
It’s a question football fans around the world are starting to ask – how many goals might Erling Haaland score in this City side?
He has scored goals wherever he has played – everyone knows that – but this City team means the level of service he is receiving is up a couple of rungs at least.
Now, five games into the Premier League season, he has a competition record of nine goals – and it could be argued he’s just got going.
It’s a frightening thought, but Haaland looks capable of rewriting the history books when it comes to scoring goals.
ALVAREZ ANNOUNCES HIS ARRIVAL...
While Erling Haaland's hat-trick will grab the headlines, Julian Alvarez's performance against Forest was not far behind his team-mate's.
Two goals, a woodwork strike and lots of good work on and off the ball suggest the Argentine is settling in just fine at City.
And there was more than a touch of Sergio Aguero in the way he took his second goal, too.
Not a bad way to mark your first full home Premier League game!
Star man: Erling Haaland
How – again – could it be anyone else?
Boss delighted with clean sheet...
"There are two things we have to control. Set pieces and transitions. We couldn't do it against Newcastle and Crystal Palace.
"We are able to do it and we can control it. The numbers (of goals we have scored) are the numbers.
"They are prolific. We can not survive conceding three goals in Newcastle, two goals against Palace.
"We have to be solid, win the ball, win the duels and especially the transitions. A team like Forest use the strikers who are quick.
"We have spoken a lot in the last two games about these concepts. We have to be solid, the defenders have to build up.
"But 19 goals in five games is the quality of the players we have."
What it means…
City's unbeaten start to the season continues with 13 points out of a possible 15 and goal difference of 14.
Arsenal's 2-1 win over Aston Villa means they are still two points clear at the top of the Premier League.
City travel to the Midlands to take on Aston Villa on Saturday, 3 September with a 17:30 (BST) kick-off.
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