Gary Cahill believes Chelsea face the ultimate challenge when travelling to prolific Premier League leaders Manchester City on Monday.
Chelsea on Wednesday night recorded a seventh clean sheet in nine games in all competitions in a goalless draw with West Ham which left Jose Mourinho so frustrated he described Sam Allardyce's tactics as from the 19th century.
The Hammers conceded nine goals to City in the two-legged Capital One Cup semi-final, yet showed a defensive resilience against Chelsea which saw Mourinho's men concede two points in the title race.
City, who Chelsea beat at Stamford Bridge in October, boast a 100 per cent record from 11 home games, scoring 42 goals in the process, and overtook Arsenal in the standings by winning 5-1 at Tottenham on Wednesday night.
Monday's contest at the Etihad Stadium will be a battle of the league's most miserly defence - Chelsea having conceded 20 goals in their 23 games - and the most prolific attack.
Cahill told Chelsea TV: "They're banging goals in left, right and centre. It's going to be really tough.
"We had a really good result against them at home; away from home (at the Etihad Stadium) they've been so, so strong.
"I suppose it's the ultimate test. It's going to be a really, really tough game.
"We've got to try to look forward to those games and going there on Monday is exciting."
Chelsea have beaten City, Manchester United and Liverpool at home, while recording away draws at Old Trafford, against Tottenham at White Hart Lane and at the Emirates Stadium.
Mourinho, whose side also travel to City in the FA Cup, would perhaps be happy with another draw, but midfielder John Obi Mikel is optimistic of more, even if he suggested a defensive approach like the one deployed against United and Arsenal.
"We have to have the belief that we can go there and win, that we can go there and play the way they play," Mikel told Chelsea TV.
"We have to go out there and believe we can stop them from scoring.
"If we can get one or two chances we can put it in the back of the net and game over."
Chelsea's revival after a November and December wobble came when Mourinho emphasised defensive steel at Arsenal and since the Blues have conceded just twice to claim the best defensive record in the league.
"It's something to be proud of," Cahill added. "As a collective unit, as a whole team, we're working really hard defensively, not just at the back."
Chelsea were unable to show the attacking ruthlessness of City against West Ham, though.
Cahill added: "We've been playing really well of late (and) it's frustrating because they killed the game off.
"They must've wasted 20 minutes of the game from setting up set-pieces and goal kicks and all the rest of it.
"On another day we score that one goal and it's game over."
Mourinho believes he has completed his business for the January transfer window, unless exceptional circumstances dictate otherwise.
For Allardyce, who is awaiting confirmation of the full extent of injuries to Joey O'Brien (dislocated shoulder) and Mohamed Diame (knee), the situation is the same as his 25-man squad is full.
West Ham now enter Saturday's home match with Swansea in buoyant mood, despite still being in the relegation zone.
Allardyce said: "We've played the last two away games and got four points.
"Let's start doing it at home, starting on Saturday, to relieve the pressure that we're under."
Adrian, who had a fine game in goal for the Hammers, added on whufc.com: "We've gone through the game without conceding a goal, which is great, and we'll look to build on that against Swansea now.
"It is an important game, because we are playing at home and we need three points more to get us away from the bottom of the table."