Chelsea defender Gary Cahill admits his side's crunch clash with Manchester City on Monday will be the ultimate test of their Premier League title credentials.
City swept to the top of the table with a 5-1 demolition of Tottenham in midweek, while Chelsea lost ground in the title race after being held to a frustrating goalless draw at home to West Ham.
Jose Mourinho's third-placed team trail leaders City by three points and a defeat at Eastlands would be a major blow to Chelsea's hopes of winning the English crown for the first time since 2010.
Mourinho accused West Ham of playing "football from the 19th century" after the east Londoners settled for a cautious approach in midweek, but City's dazzling array of attacking talent may force the Chelsea boss to adopt a conservative gameplan himself.
The Blues have already beaten Manuel Pellegrini's side this season when a Joe Hart error allowed Fernando Torres to a score a late winner at Stamford Bridge in October.
But City have been in majestic form since then and their five-star display at White Hart Lane extended their unbeaten run to 20 matches in all competitions.
Pellegrini's men have scored a remarkable 115 goals this season and have been invincible at Eastlands, crushing all opposition to record a 100 percent record of 11 wins on home turf in the Premier League.
Even the country's best teams have been embarrassed at Eastlands, with Manchester United conceding four and Arsenal and Tottenham both hit for six.
England international Cahill acknowledges Chelsea, who will move level on points with City if they win, will have to produce their very best to emerge from Eastlands undefeated.
"They're banging goals in left, right and centre. It's going to be really tough," Cahill said.
"We had a really good result against them at our place but at home they've been so strong.
"I suppose it's the ultimate test. It's going to be a really, really tough game."
If City striker Sergio Aguero fails to recover from a hamstring injury, Pellegrini will choose between Alvaro Negredo or Stevan Jovetic as his replacement.
Jovetic replaced Aguero at Tottenham and notched his first Premier League goal since his £22 million ($36mn, 27mn euros) transfer from Fiorentina last year.
The Montenegro forward, who is finally fit after battling injury and illness, warned his team-mates to guard against over-inflated expectations after a host of pundits this week labelled them champions elect.
"We were really happy after beating Tottenham but we need to stay calm because nothing is finished," Jovetic said.
"The next one against Chelsea is going to be a crucial game. I hope we will play like we did against Tottenham.
"At the moment, everything is perfect but we need to do our job as we did until now and like this we can be successful."