This dismantling of Southampton illustrates how difficult dethroning Manchester City will surely be. From opening whistle to the last Pep Guardiola’s side made the contest a duck shoot on an afternoon when Raheem Sterling was sublime.

The forward scored twice and helped create three more, and at 23 is only going to improve. So, too, a City whose prevailing characteristic is the embodiment of their manager’s relentlessness. Guardiola’s assessment underlined this, agreeing that most opponents should be frightened of City – but only regarding their opening.

“The first 20 minutes, yeah,” he said. “We were lucky to score the fourth goal at the last minute of the first half [to make it 4-1] because I had the feeling the game was not over. We played with the ball so good but not without the ball. We were not stable behind [defence]. The team showed me some signals that in some positions we are not stable enough.”

Guardiola believes Sterling can be as fine a footballer as he wishes to be having overcome a fear of shooting during the Catalan’s first season. Then Sterling managed 10, before registering 23 last term, and he now has six in this one. “His head [mentality] has changed,” said the manager. “The first season, he was scared, was looking – who is the guy I am going to pass to? We spoke and said try to score goals. He is becoming a winning player.

“He is stable and is focused on what he has to do to become a better player. He is a top player but still so young to consider [being] the world’s best. Still he can lose simple balls.”

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City pinned their opponents back instantly from the kick-off. A moment of mild panic from Saints in the area was followed a few moments later by a free-kick. It was hit in from the right by David Silva and though it came to nothing the terms between the sides were about to change.

It took six minutes and already cast the contest as a mismatch of Anthony Joshua versus junior-flyweight proportions. Leroy Sané was Guardiola’s sole change from the XI that won at Wembley against Tottenham in their last league outing and promptly showed why he was back.

After James Ward-Prowse stepped on the ball Sergio Agüero fed Silva and his pass slid Sané in along the left. In a flash the ball was whipped in and a hapless Wesley Hoedt smashed home for an own goal.

Mark Hughes’s men were still reeling when the champions doubled their lead. This time Sterling was provider. The winger appeared to have overrun the ball but managed to turn it across goal and there was Agüero to notch a 150th Premier League goal.

The 30-year-old has achieved this in 217 appearances, second only to Alan Shearer’s 212, and had time to miss a golden chance for a second – he hit Alex McCarthy’s legs – before City went 3-0 ahead. Sterling and Sané were again to the fore: the former chipped towards the German and when the ball bounced Silva volleyed it in.

City did not face a threat until the 26th minute and it proved an augury of Danny Ings’s penalty strike moments later. When Shane Long crossed, the visiting No 9 was unmarked but could not capitalise.

He was about to do better. Ings raced on to a Ryan Bertrand pass along the left and John Stones might have whacked the ball clear. Instead, perhaps due to an Ederson call, he left it to the goalkeeper and as Ings ran on he was pulled down by the Brazilian. The referee, Lee Mason, pointed to the spot and Ings converted for City to concede only a fourth goal in the league, and a first since Newcastle United scored here on 1 September.

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As half-time approached the home side offered a telling sequence. This was a mesmerising display of passing that took place in the tightest of spaces inside Southampton’s area. Sterling to Sané to Sterling to Sané. He now fed Agüero who nutmegged Hoedt and found Silva. He in turn found Sané who relayed the ball to Kyle Walker who finally took aim, but to no avail.

Now, though, came further hurt for the visitors. Agüero picked Cédric Soares’s pocket and turned the ball in from the left. It came to Sterling and his miscontrol worked to his advantage as he gained space and time to collect a fifth of his league campaign.

In the second half Guardiola switched Sterling and Sané to the opposite flanks and just after the hour reward nearly came. Agüero fed Sané on the right and the German had a shot that crashed back off McCarthy’s right-hand post. Sterling’s afternoon to remember became even better on 67 minutes when he beat McCarthy for a second time.

By the close Sané had made it 6-1 – courtesy of Sterling’s final assist – and City had signalled that they may be even better than last season’s record-breaking champions. It left Hughes frustrated. “We weren’t strong enough in the opening period,” he said.