The Hammers will arrive at White Hart Lane this weekend perched one place and two points above their capital rivals in the Premier League standings.
Sam Allardyce's side will also be feeling a lot better about themselves when they make the short trip to north London, with only three defeats suffered in 12 outings so far.
In contrast, Spurs have already come undone on five occasions and have yet to display any kind of consistency under new boss Andre Villas-Boas.
McCarthy believes that could play into West Ham's hands, saying: "We can take heart from our second half performance against Stoke City and go into Sunday's game with a bit of confidence.
"Tottenham are a bit shaky at the moment and we will be going to win the game and I think the way we are playing at the minute, they are going to find it difficult to beat us."
On a daunting run of fixtures which will see the Hammers face Manchester United, West Bromwich Albion, Liverpool and Chelsea after tackling Spurs, McCartney added: "Obviously it is going to be a difficult run, but it is all about the teams coming up next.
"It is one game at a time and it is Spurs on Sunday. It is a big derby and everyone will be up for it.
"It is going to be a tough game and there are tougher ones after that, but hopefully we can build on the 19 points we already have and stay in the top half."