“I try to be very open,” sighed a weary looking Slaven Bilic. “I try to be honest as I always am. It ain’t helping if we are trying to wrap things in paper and to hide. We can’t continue like this. We can’t.”

As brutal self-assessments go, the West Ham United manager’s mea culpa – including an apology to his pet dog – in the bowels of the London Stadium after his side’s 5-1 capitulation against Arsenal was hard to beat. A crestfallen Angelo Ogbonna, shoulders slumped after his mistake handed Mesut Özil the opening goal to silence further a strangely muted atmosphere for the first London derby in the Premier League to be played in their new home, was just as frank.

“The expectations were so high,” he said. “There has been a lot of change – new stadium, training ground, new players. Maybe we relax a bit. But this is now December and we need to get back. I can talk until the end but any phrases are not important.”

It was not supposed to be like this. Back in April at Upton Park a hat-trick from Andy Carroll lifted West Ham from two goals down against Arsenal to a thrilling 3-3 draw that maintained sixth place in the table. Before the long-awaited move to the stadium that hosted the 2012 Olympics the club announced they had sold 50,000 season tickets and hailed “the biggest and most successful stadium move in Britain in the modern era”.

“Without doubt our stadium move is an unrivalled success story but we know the hard work does not stop now,” the vice-chairman, Karren Brady, said. “We must deliver a stadium that exceeds our season ticket holders’ expectations and support Slaven Bilic in building a team on the pitch that matches our stunning new home.”

Quite what Brady and the co‑chairmen, David Gold and David Sullivan, must have been thinking as Alexis Sánchez slammed home Arsenal’s fifth goal one can only speculate. But Bilic – looking lost in his own thoughts as he stood in the exposed technical area of the London Stadium’s wide open spaces – knows only too well where this is heading.

The loss of James Collins to injury inside the opening seven minutes encapsulated the dreadful luck the manager has endured this season, with his replacement, Álvaro Arbeloa, repeatedly exposed by an Arsenal side who never needed to find anything more than second gear. Yet it was the manner of a performance horribly lacking in the kind of passion that inspired the comeback against the same opponents in April which will concern those 50,000 season-ticket holders most.

At times the atmosphere in the stands felt more like being at a Keane concert at the O 2 than a match between two old London rivals and the exodus when Sánchez made it 2-0 with 18 minutes left to play spoke volumes.

“I must say that usually the West Ham fans are very loud. And they were ready tonight,” Arsène Wenger said. “But they were never in a position where they could let it go out because we were always leading. They have to recreate something where people share the experiences and the players feel completely the confidence that they are playing at home and not on a neutral ground. It takes two years.”

Bilic definitely does not have that long. Only one point separates West Ham from the bottom three but after the trip to face Liverpool at Anfield next week, home games against Burnley and Hull City could decide his fate in the short term. Asked how much credit he has with the owners after last season’s seventh place, he was suitably diplomatic. “That is not a question for me. And I don’t think [about it] and that is the good thing. I don’t think about that. What is going to happen with this. Or how many more games I have until your next contract talks, your chop or sacking, whatever. I don’t think that way. As I told you, I feel positive, I feel very brave as a person and as a coach and as a manager.”

Finding a regular striker to convert the chances created by Dimitri Payet and Manuel Lanzini will be a priority, although Carroll’s consolation goal on his latest comeback from injury could bode well. Of more immediate concern is the leaky defence and extensive injury list, even if Bilic was dismissive of any excuses. “It’s very simple: we have to work hard. There is no secret. We have to,” he said.

“We changed the system, we changed the personnel, we turned things around at the club, we used a lot of players. Some of the players are back from injury, some of the players are new. Rotation, everything, blah, blah, blah. To try to provoke and force something new.

“I am positive that we aren’t going to be in this situation in one month, two months, three months. Especially not in May. But we are talking about now. And I have absolutely no problem in [saying we are in a relegation battle]. What should I say? That we are not in this situation when we are? I think it’s way better to say we are, to say: ‘Listen guys, including to the journalists and players, manager’s staff, our wives, our dogs. We are. We are in that situation. Only then, when you realise you are in that situation, can you change it.”