The visitors looked to be on their way to a Premier League victory at Anfield when Olivier Giroud put them 2-1 to the good in the 64th minute after Mathieu Debuchy had cancelled out Philippe Coutinho's opener.
But Skrtel, whose head injury had caused a lengthy delay early in the second half, nodded in Lallana's corner in the seventh of nine additional minutes to salvage a point for the hosts.
Arsenal stay seventh in the Premier League as a result of the stalemate, which left Wenger to rue his side's inability to defend from dead-ball situations.
"It was maybe a fair result, but we are disappointed to give a goal away with a free header from a corner," Wenger told BBC Sport.
"It was an intense game. We played a little bit with a handbrake in the first half. Liverpool played well. We lost the ball too quickly in the first half - when you are not used to something it was frustrating.
"In the long stoppage time you have to survive two three corners and free-kicks. For their goal, we had plenty of defenders on the pitch.
"It's disappointing that we didn't even jump. You want everybody to be focused on the corner."
‘He instantly popped into our ratings as one of the best U21 midfielders in Europe. The impressive thing is Slot has made him into more of a no.6' Inside Ryan Gravenberch's transformation at Liverpool
‘I don’t think Liverpool would look at Ollie Watkins, a striker isn’t a pressing issue for them – it’s Arsenal who need one’ Former Reds star explains why his old club don’t need an out-and-out forward this summer
