The Gunners were blown away 5-1 at Anfield.
"We are very disappointed, especially with the first half," Oxlade-Chamberlain told arsenal.com.
"We know we are better than that so in that sense we are gutted.
"But these things happen in football and it is our responsibility to turn that around and we have great opportunity on Wednesday night.
"When the first goal went early (in the first minute) you have to respond and 'see out' the next 10 or 15 minutes.
"We failed to do that and, credit to Liverpool, I thought they were brilliant and we were not up to scratch.
"In the second half we knew we had to improve and I believe that we did that.
"So there are some mental positives but we have to put it right on Wednesday."