At the halfway stage of the season Liverpool are five points adrift of both the visitors and Birmingham as they attempt to retain the title.
And 25-year-old Longhurst thinks Liverpool’s championship aspirations could depend on a positive result against her old side.
“Without putting too much pressure on us I think it is a must-win game,” Longhurst told Sky Sports.
“It’s really important we get the three points, get ourselves going and put some real pressure on the teams above us.
“For us to have a chance of winning the league this year and be in with a shout of finishing in the Champions League places we have to look to get the win.
“We can’t afford to let Birmingham and Chelsea stay ahead of us for too much longer really so hopefully we can make three points up on the this weekend.”
The Chelmsford-born striker was reunited with former Chelsea manager Matt Beard when she made the move from south-west London to Liverpool before the start of last season.
Longhurst is one of three Liverpool players who have previously turned out for Chelsea but insists the former Blues contingent will be treating this game like any other.
“I really enjoyed my time at Chelsea but I just wanted the chance to experience something different and for me it was great opportunity to come up here,” she said.
“Beardy was there for a while so I know this game will mean a lot to him and of course Gemma was there and Fara but we just have to look at it as another game where we really need to get three points.”
The former Colchester and Millwall striker has called on the fans – who she calls the best in the country - to summon the spirit of Anfield and act as the 12th woman for the Ladies.
“We’ve got great fans who I think are the best in the league,” Longhurst added. “I’ve not been to a ground where the fans are as good as ours.
“They sing our names and they are passionate and they care about us. Every time we play we’re not just playing for us – we’re playing for them as well.
“We’ll definitely need them to be at their loudest and at their best to help us get over the finish line and get three points against Chelsea.”