The fragile truce between José Mourinho and Arsène Wenger has finally been shattered after the Chelsea manager denounced his counterpart at Arsenal as "a specialist in failure".

In a verbal attack reminiscent of the regular spats between the pair during Mourinho's first spell in English football, when he had once infamously declared Wenger a "voyeur" obsessed with watching Chelsea from afar, the Portuguese claimed his rival still "loves to look at this football club".

The Portuguese pointed to Arsenal's eight-season period without a trophy as evidence of real failure, and claimed he would have walked away from a club if he had gone four years, the length of his current contract, without winning one.

Mourinho was responding to comments from Wenger earlier in the day when the Frenchman, without mentioning his direct rival by name, had suggested rival managers' unwillingness to admit their teams are contenders for the Premier League title was born of a "fear to fail".

"If you declare yourself not in the race, you cannot lose it, simple as that," Wenger had said. "I just think our job is to be ambitious and to try to win. And if we do not win, to take full responsibility for that. It's very difficult when you're first in the league to distract people."

Chelsea currently top the table, with Wenger having made clear even back on new year's eve that he did was giving short shrift to Mourinho's regular insistence that his team were unlikely title challengers. Yet the implication of his words clearly struck a nerve. "He is a specialist in failure, I'm not," retorted the Portuguese. "So if supposing Wenger's right and I'm afraid of failure, it's because I don't fail many times. So maybe he's right. I'm not used to failing. But the reality is he's a specialist because, eight years without a piece of silverware, that's failure. If I did that in Chelsea I'd leave London and not come back."

Asked if Wenger's comments had annoyed him, Mourinho said: "Yes. He loves to look at this football club. I thought between 2007 and 2013 [when the Portuguese was at Internazionale and Real Madrid] was enough time for Wenger to forget this. But it looks like he always likes to look at this club. Am I afraid of failure? What is that. I believe at the end of the day I'll be seen as the 'impolite guy', the one who's aggressive in his words. But I'm not.

"He is saying we're not candidates because we're afraid of failure? Failure of what? Not winning a title this year? Or in two years? I have a lot of respect for him, he's a great coach, but failure is not winning a title in seven or eight years. That's failure. Am I aggressive in my words? I don't know. Ask him, not me [why he is obsessed with Chelsea]."

Mourinho expressed regret at having used the word "voyeur" in an outburst back in October 2005 about what he perceived to have been Wenger's regular commentary on events at Stamford Bridge. "I'm very sorry for that, so sorry for that," he said. But he failed to disguise his astonishment that the Frenchman had been allowed to go eight years since winning the 2005 FA Cup without winning another cup.

"If I don't win a trophy in four years, I don't want a new contract," he added. "It's as simple as that. I don't think a manager should be embarrassed when he gives everything, tries everything, dedicates himself to the club, the project and the collective dream. If you don't get results, that's football. But for my mentality – my mentality – there is a limit. There is a limit. And you have to be strong enough and proud enough to admit when it's enough.

"In eight years you have to build so much, so much, so much. The club gave me a four-year contract – four years, no? [he sought clarification from Chelsea's head of communications at his side] – and that's the period where I want to give everything and try to get results. If I don't, I think that's normal [to leave]. That's normal in football."