Braces from Martin Skrtel and Raheem Sterling, plus another strike from Daniel Sturridge, saw the Reds to a famous win over the side leading the way in the standings at the start of the day.
A number of errors contributed to the Gunners' miserable afternoon on Merseyside, and the experienced Frenchman admitted to being concerned by what he saw from his players.
"It was a very poor day. We were poor defensively, offensively," Wenger told BT Sport.
"Liverpool played very well, so congratulations to them. But it was a poor performance on a day when we couldn't afford it.
"Of course it raises some questions today because we were caught many times and were naive."
Asked how he would look to right the wrongs, Wenger added: "Defensively we need to be more stable. Today we were too open. From the front to the back we were not at the level we are used to."
Opposite number Brendan Rodgers was understandably thrilled by a performance that saw the Anfield side close to within five points of the Gunners, although he refused to accept the result put his troops back in the title hunt.
"It was an incredible performance," he said.
"It's not the first time we've been outstanding at home, but everything about us today was incredible. Everything was outstanding.
"We've been getting better and better. We've got a lot of young players, developing well. But for us it's just about improving."
Sturridge, who scored Liverpool's fourth goal with just 20 minutes on the clock, added: "We went out and did what the manager told us to do. The first 20 minutes we were unbelievable.
"The boys all over the field, every player, has done fantastic over the last couple of games, but we won't get too excited."