Winger Solly March (28) scored twice and created a third for Brighton as they dominated the game from start to finish, with Liverpool barely able to string together a single decent attack.
"Massively frustrated, congratulations to Brighton on a super game against a bad opponent. We were not good today, I can't remember a good phase or period," an irate Klopp said.
"Doing better than today should be easy because this is a really low point. I can't remember a worse game," he added.
Despite losing 3-1 to Brentford in their last Premier League game on January 2, Klopp said that he had been confident coming into Saturday's game that his side could get a much-needed win.
"There was no sign for this performance before the game, but that's probably how it is sometimes. There's nothing that I thought yesterday or this morning that this could happen."
Liverpool's campaign has been derailed by poor performances and injuries to key players, with captain Virgil van Dijk (31) missing due to a hamstring strain and recent signing Cody Gakpo (23) starting up front due to the absence of Darwin Nunez (23).
As a result, the Reds struggled to maintain possession and Brighton were able to make the most of the chances they were offered.
"In these moments we passed from the last line up front, and then when we want to push up the ball was already gone again. So that's why it's just counter (attacks) from their side and it always looks horrible," Klopp said.
Liverpool are eighth in the table on 28 points, seven behind fourth-placed Newcastle United, who currently occupy the last Champions League place.
