Manchester City can't say Liverpool didn't warn them. They said they had a plan to stop Erling Haaland, explained how they were going to do it, and then produced a near-perfect defensive performance on the day to do just that.
In the process, they repeated their feat from the Community Shield and stopped Haaland from scoring, joining Bournemouth as the only Premier League side to keep the Norwegian from finding the back of the net. They also prevented him from providing an assist, which Bournemouth couldn't, and claimed three points over City which also can't be said of the Cherries.
That Community Shield blank for Haaland was an anomaly, and there were clear mitigating factors in that he had only played 40 minutes of pre-season football before that, and Liverpool were significantly fitter than the Blues that day owing to contrasting pre-season schedules. Haaland's Anfield blank was a much more impressive feat from Liverpool - but how did they do it?