Slaven Bilic insists Jose Mourinho is still the best manager around.
The Portuguese finds himself under scrutiny following Chelsea's poor start to the season, with the reigning champions down in 12th place after just three wins from their opening nine games.
West Ham, by contrast, are flying high in fourth spot after a sparkling start to Bilic's reign at Upton Park.
But as the Hammers prepare to host Mourinho's men on Saturday, Bilic is backing his opposite number to guide them back into the top four this season.
"It's a big challenge for us, it's a big test," the Croatian said. "It's a special game because they are the champions.
"And you can easily say he is the best manager around. He's been doing it all his career, he's brilliant. He's Jose Mourinho!
"It just shows how strange football is. It's the same team, the champions.
"I know Mourinho and he's always motivated. His teams are always hungry and everyone expected them, maybe not to be top after nine games, but not to be where they are now.
"But sometimes in football it happens. I watched most of their games.
"Sometimes you play the same way but you hit the post and the opposition don't hit the post, when last year it happened the other way round.
"It doesn't have to be anything major. You lose a couple of games - and from their point of view drawing is like losing - and suddenly people say 'what happened to Chelsea?' but it's nothing big or major.
"If it was he would be the first to change it, but sometimes it's those invisible things you can't detect and you have to work hard to try to change it.
"Things will definitely change for them, we just hope it won't be against us. I see them finishing in the top four."
West Ham will be without winger Victor Moses under the terms of his loan deal from Stamford Bridge, while defender Winston Reid has yet to shake off the knock which kept him out at Crystal Palace last week.