Ange Postecoglou has opened up on the exasperation he feels at the softness of his Tottenham team in particular moments, which he suggested was linked to mentality. The manager refuses to believe there is an “institutionalised” reason for the club to fall short of their targets and said he would never “palm off responsibility to whatever we’re going through to things that have existed in the past”.

But as he looked forward to Sunday’s derby at home to Chelsea, he lingered on the frustration of Thursday’s 1-0 defeat at Bournemouth. After it, some of the travelling support directed abuse at him. What drove Postecoglou to distraction was how, after a reasonable start, his team conceded at the first sign of pressure – allowing Dean Huijsen a free run to head in from a 17th-minute corner.

It was Spurs’ third loss in six Premier League games, each against teams that started below them; relegation-threatened Crystal Palace and Ipswich inflicted the others. Spurs, who are 10th, have beaten fourth-placed Manchester City and eighth-placed Aston Villa during the sequence. They drew with Fulham, who are sixth.

“The key is to understand that Bournemouth is not a ‘lesser’ team,” Postecoglou said. “They have beaten City and Arsenal at home. We prepared ourselves for a tough game, that was going to be tougher than any other game we were going to face.

“And the disappointing thing is that in a game where we started well, we once again allowed the opposition to play the game on their terms by us lacking discipline and conviction in a key moment. We can’t keep doing that.”

Postecoglou was asked whether it was a physical issue, one to do with mentality or a mixture of things. “It’s a bit of everything but it can’t be a physical thing when it happens early in the game,” he replied. “We started well. And literally the first time they go up, they get a set piece and they score an unopposed header. You can’t go into a game like that and allow the opposition then to take control.

“It doesn’t sit well with me. Nor should it. I’m not going to accept it. My responsibility is to change that because if we’re going to get to where I want us to get to, we need to break that cycle of not showing the belief and resilience in key moments.

“Nothing’s changed in terms of my resolve to play the football I want to play. It’s just that we haven’t understood the other side of that and that’s the discipline and resilience to overcome difficult moments so that football we have can come through.”

When Spurs prepared for last season’s home fixture with Chelsea at the beginning of November, they were top of the league with eight wins and two draws from 10 games. On a wild night, they sustained two injuries and had two men sent off and still carried the fight, the defining image coming when seven of their outfield players pushed up on the halfway line as Chelsea attacked. Spurs lost 4-1, the final two Chelsea goals scored in stoppage time, but Postecoglou’s team were applauded off.

Nobody would see the positives in a defeat this time because the climate has changed, the mood as edgy as Spurs have been inconsistent. Including that Chelsea game, Spurs’ record in the league since then reads: W18 D6 L18.

“It’s about winning but it’s about belief in what you’re doing sometimes,” Postecoglou said. “You look beyond the results. That’s what happened at the start of my tenure last year. We lost against Chelsea but there was a sense that we were building something. Obviously it kind of went off the rails after that game. It’s not just about winning but where we are right now it will certainly help.”

Postecoglou said two weeks ago that if Spurs were 10th at Christmas, there would be “a lot of scrutiny” around his position. They go to Southampton in the league next Sunday before hosting Liverpool on the Sunday after that.

The injuries have piled up, Ben Davies the latest to go down, to a hamstring problem at Bournemouth. Postecoglou would like to welcome back Cristian Romero, who is scheduled to train on Saturday as he tries to overcome toe and hamstring problems.

Postecoglou said he had not yet worked out why the team had been so erratic. “We will keep searching for those answers. Some of it is just around having a competitive squad where there is competition for places which keeps people on edge and we don’t have that at the moment. We haven’t had that for a while. Within the absence of that, we have to find other ways to make sure the players are clear on their responsibilities.”

Postecoglou is clear that the bucks stops with him. He said if there was doubt – “whether that’s internally or externally” – it only hardened his resolve to get it right. On the other hand, it was plainly better if the fans backed him; otherwise the culture would become toxic.

“Sometimes it doesn’t work out that way so I’ve got to find a way to make that happen.”