Gabriel Magalhaes led Arsenal to a hard-fought 1-0 victory over Tottenham in a heated North London derby on Super Sunday.
From Spurs' perspective, it was the 16th set-piece goal they have conceded this calendar year. Even more damning is that, since the turn of the year, Postecoglou's side have conceded 13 times from corners - the second-highest total in the division.
Postecoglou in May said "he wasn't interested" about his side's weakness while defending set-pieces and he was similarly prickly when pressed on the subject in his post-match press conference following the Arsenal defeat.
He said: "I know for some reason people think I don't care about set-pieces, and it's a narrative that you can keep going on for ages and ages. I understand that.
Trending"Like I said, we work on them all the time, like we do with every other team.
"You know that they're a threat. As I said, for the most part we handled them really well today, but we switched off in one and we paid a price. You learn from that and you move on.
"It is what it is. It's my burden to carry and I'm happy to do that. Like I've always said, for me there's a bigger picture that's at play here that's much more important than the finer details of us getting to where we want to.
"For us, the way forward is to, as I said, try and turn the football we're playing now into something meaningful.
"We're a team that's progressing in many areas. With all that sort of progress, there's always kind of new challenges and new things that you need to overcome.
"When I look at the four games in isolation this year, our football's been more consistent and more compelling than it was in our first four games last year. Obviously the results don't reflect that.
"I think we've made progress in certain areas, but there's other areas, like I said, we still need to improve on. That's my job, to kind of fill those gaps as quickly as possible."
Jamie Redknapp on :
"It is Spurs' kryptonite. They cannot defend from corners, but Arsenal and Aston Villa are the best at corners - the detail, good delivery in, they are attacking the bal.,
"Arsenal were unlucky in the first half, but with the right delivery in the second half from [Bukayo] Saka and Gabriel is just too strong for [Cristian] Romero and it is a fantastic header."
Gary Neville speaking on The Gary Neville Podcast:
"It's poor defending from Romero. He has got to stay tight to Gabriel. I will go hard on the goalkeeper. I played with dominant and not so dominant goalkeepers, and it's an absolute must for me to have a goalkeeper that's brave.
"He was a yard or so off his line, but he was getting involved. That ball lands three or four yards in your zone, and I'm not having this idea that goalkeepers get blocked.
"The great goalkeepers, if they get blocked, it's a foul and a whistle will go. He has to come out and punch that. He has to help Romero. That's the expectation of me as a defender that my goalkeeper has to come out and catch it or punch if it's three or four yards out from the centre of the goal.
"I don't care how it's being played in, your starting position should be one or two yards out, you should be able to step and catch or punch. The idea that he gets involved all the time, he's pontificating, he's always whinging before the ball comes in, his arms are everywhere, he's a bit frantic. I don't want to see that.
"The best goalkeepers will come out the odd time and flap and miss, but that doesn't stop them from doing the right thing the next time.
"You don't want an emotional goalkeeper in my opinion. You want calmness. It's a rock, it's your last line of defence. I don't want them shouting and putting their arms everywhere because it creates anxiety in the crowd and with your defenders. I wanted him to be more dominant."
' Nick Wright:
It was probably fitting that the game was decided by a set-piece. One of Arsenal's biggest strengths remains a perplexing weakness for Postecoglou's Spurs.
Gabriel's header, powered home from inside the Spurs six-yard box from Saka's inswinging delivery, was the 22nd set-piece goal Arsenal have scored in the Premier League since the start of last season, the most by any side in the division.
The writing had been on the wall, with Arsenal causing repeated problems from corners even before Gabriel made the breakthrough. A major weapon for Arteta's side remains a fatal weakness for their north London rivals.
Three of Arsenal's last four Premier League goals against rivals Tottenham have been from corners - the same number of corner goals they scored in the previous 88 North London derbies combined.
Tottenham captain Heung-Min Son to :
"The football was there, we dominated the game. It was the lack of details and we conceded two goals last season to set-pieces and today is also about set-pieces.
"That's the details that change results in big games. It's a painful result and I'm sure the fans are very, very disappointed.
"We need to improve, 100 per cent, and move on. In tough moments, we have to stick together.
"We are getting in the final third, we are making the right shots and right decisions. But the players have to take responsibility because that's the hardest part. We showed it in training and in the games, we need to be more clinical.
"Early in the season, it's a tough moment definitely. We have to stick together and then if we get good results, we will bounce back stronger.
"We have to take responsibility, there's nothing else to say. The belief is there, the football is there. We have to be more clinical."