Rafa Benitez's side are just four points behind Manchester City going into Sunday's intriguing clash at the Etihad Stadium.
Defending European champions Chelsea must first face Sparta Prague in the second leg of their Europa League last 32 game but Cahill already has one eye on the crucial domestic fixture at the weekend.
"We've obviously got a huge game tomorrow night, and then a massive game on Sunday," said Cahill.
"If we get a positive result on Sunday then that opens it right back up. We're taking it one game at a time but we'll be looking to do that.
"It'll be tough game away from home, but if we do get a positive result then obviously second place is within touching distance."
Cahill recognises the importance of focusing on the game against Sparta first though, with the Blues taking a 1-0 lead into the home leg at Stamford Bridge thanks to a goal from Oscar in the opening leg.
"You've always got to take teams seriously. They're a quality outfit, and made it tough for us away from home," he added.
"But we got a positive result, the away goal, but we still won't take it lightly. They've got some great players. Our home form in Europe is nine unbeaten, so hopefully that can continue."
Cahill also paid tribute to John Terry, who may partner him in the heart of the defence as he continues to work his way back from a knee injury.
"He's a massive character and leader for us. He's been struggling with his injury a bit, but has come back again," said Cahill.
"It's just great to have everyone back fit. You don't want people sitting in the treatment room if you can help.
"To have most of the lads back out there with us now is a healthy situation."