The England winger grabbed both goals in a 2-0 home win at the Emirates Stadium to move the Gunners into the quarter-finals of a competition Wenger has never won.
And speaking after Oxlade-Chamberlain's inspired performance, the Arsenal boss hailed his player's attitude.
"His concentration is sharper, he is more determined and he has worked very hard in training," he said. "That is now showing on the pitch."
Wenger also had praise for the other stars of an experimental side, with Carl Jenkinson - returning to the team after two years out on loan - among them.
"It's fantastic to see Carl back," he said. "He did well and had no fitness problems at all, which shows that he prepared well.
"I felt Rob [Holding] did well, Ainsley [Maitland-Niles] played some nice passes and Jeff [Reine-Adelaide] had a good game, too."