The Fifers were once again unable to put clear daylight between themselves and those chasing fourth spot.
East Fife currently sit in the final remaining play-off place but Annan, East Stirling, Elgin and now Berwick are all within just a few points.
Three times this month the Fifers have been beaten and on all occasions passed up the opportunity to stretch their point advantage over the rest.
Berwick arrived at Bayview knowing defeat would push them 10 points adrift of the play-off zone and out of the race.
They played like a team possessed, while East Fife looked sluggish.
Boss Gary Naysmith conceded after the game that he believed some of his players may have thought their place in the play-offs were a shoe-in after their win over Arbroath on Saturday.
A first half strike from Paul Willis put Berwick on their way to the three points before Kyle Wilkie, Blair Henderson and David Gold completed the job in the second 45.
Sean Dickson bundled a late counter back for East Fife.
Naysmith said following the game that any hit of complacency in his side would be swiftly removed.
He said: “It’s not good enough - Berwick deserved their win and looked the hungrier team.
“We looked as if we were going through the motions and that fourth place had already been secured.
“Berwick played as though they had a cause.
“We started with nine of the team which put in such a good performance on Saturday but, for every positive we took from Saturday, the opposite applied.
“We were second to every ball and they looked hungrier and fitter.
“If we’re being honest, we’re lucky it was only 4-1.
“That’s twice in the last three weeks that I’ve had to say it’s not good enough.
“I pick the team and I thought it was quite an easy one to pick after Saturday.
“They were told in the team talk that we had a chance to open up a good gap and everybody else would be looking at it thinking ‘it’s going to be hard to catch them’.
“We would have gone 10 points clear of Berwick but they played it like a cup final and a last chance.
“I’m hurting just now like the fans.
“We took a bit of stick at the end and rightly so because the fans came looking for a performance and we never gave them it.
“We’ll need to get to the bottom of it and get it out of our system.”