After victory over Manchester City, Chelsea boss Guus Hiddink admitted Liverpool had done them a favour with their victory at Manchester United on Saturday.
Chelsea ensured they kept up the pressure on leaders United thanks to Michael Essien's first-half winner against Manchester City at Stamford Bridge.
It put the Blues back into second place, ahead of Liverpool on goal difference, and just four points behind United.
But Hiddink was still extremely wary of United's game in hand on the rest of the chasing pack.
"If it was just four points it would be very close, but they have that game in hand," he said. "But it's clear that after Saturday's unexpected result that the tension has come back in the league.
"It's a boost. But if we want to track them, we have to keep on winning. That'll give tension to the end of the season, which is good for everyone.
"Every now and then you get a defeat you don't expect. Sometimes you don't expect it at home because you have a beautiful record, then all of a sudden it happens.
"But they're a very experienced team. Let's see how they react in the up-coming days. It's not the first time that it's happened, but the big teams always react.
"I don't know what their reaction will be. When you are in the driver's seat and someone else is coming, you can get a little bit nervous. It is a little bit open now."
