North London derby defeat raises further doubts about Ange Postecoglou | Jonathan Wilson

IIt was, as everyone had pointed out, inevitable that the north London derby would be decided by a set piece, with Gabriel heading the only goal of the second half as Tottenham in general, and Cristian Romero in particular, were eliminated. It was a victory that kept Arsenal within touching distance of Manchester City – and that it is not absurd to think in such terms even at this early stage of the season suggests how City’s ruthless excellence has affected the outlook – but it also raised further doubts about Ange Postecoglou.

Last season’s heady start, which saw Spurs take 26 points from their first 10 games under the Australian, feels a long time ago. Some regression to the mean was inevitable, but 44 points from their subsequent 32 games is a poor enough record to be cause for concern. Extrapolate that over a season and you get 52, which is what West Ham got for finishing ninth last season. For Tottenham, with their spending and their stadium, that would be far from acceptable. It’s never entirely fair to pick out isolated parts of a season, but 32 games is a fair sample.

“For some reason people think I don’t care about set pieces and it’s a story you can keep repeating for ages,” Postecoglou said on Sunday. “I understand that. We work on it all the time, like any other team. You know they are a threat, like I said, generally we dealt with them very well today, but we took them out once and we paid a price for that and you learn from that and then you move on.”

There was a definite sense of grumpiness, which is perhaps to be expected, but “for some reason” it seemed unnecessarily passive-aggressive. The reason is that Postecoglou dug himself a hole last season by saying he worked specifically on set-pieces: “I’m just not interested in it. I’ve never done that.” He did go on to clarify that, on a philosophical level, he prefers to look at the game holistically rather than offload one aspect to a specialist set-piece coach, as Arsenal did with Nicolas Jover.

“It’s something we’re working on, along with everything else in our game,” he said in May. “There are much more important things we need to focus on at the moment in terms of the team we’re building.” Assistant manager Nick Montgomery was brought in over the summer and, while not a specific set-piece coach, he appears to be the man responsible for it. But when Tottenham allow teams to overwhelm Guglielmo Vicario as Arsenal did, and when Romero is so easily brushed aside by opponents, the problem quickly becomes less about structures than about individuals.

That may be true, but as a percentage of total goals conceded, only Nottingham Forest have conceded more from set pieces than Tottenham last season – and the Premier League is unforgiving; no weakness is left unexploited. Gabriel’s goal was the first Spurs have conceded from a set piece so far this season, but there is another pattern that is just as damaging. In all four games so far this season, they have had at least 60% possession, yet they have won only one. In all four, they have been ostensibly the better team – although Newcastle ultimately recorded the better xG – but they have not created the chances they probably should have, have, apart from against Everton, failed to take their chances and have subsequently exposed their soft underbelly.

Postecoglou’s teams are usually at their best in his second season in charge: he himself alluded to this on Sunday when he corrected a journalist who had said that Postecoglou “normally” wins a trophy in his second season to stress that he “always” does it – and that has happened with South Melbourne, Brisbane Roar, Yokohama F Marinos and Celtic; for the last three of those, that trophy was the league. Even if City were to suffer a huge points deduction, it seems hard to imagine that happening this season.

But what Postecoglou must find frustrating is that his team don’t seem so far away. It sounds vaguely ridiculous to say of a team with four points, but it wouldn’t have taken much effort to get them to win four out of four at the start of this season. In the expected points world, Tottenham are just one point behind Arsenal. But in the real, actual world, they are already six points behind their rivals and four points adrift of the Champions League places. The basic processes seem to be there: they just need a little more ruthlessness, a little less rashness, a little more confidence and decisiveness. The problem is that Tottenham, of all clubs, have heard it all before: that is the essence of Spursiness.

At the start of last season, it looked like Postecoglou’s uncomplicated coarseness was just the thing to break through years of underachievement. The problem now is that, as the set-piece defending problem shows, it may have become a contributing factor.

• This is an excerpt from Soccer with Jonathan Wilson, the Guardian US’s weekly look at the game in Europe and beyond. Register here for free. Got a question for Jonathan? Email him at soccerwithjw@theguardian.com and he’ll feature the best answer in a future edition