George Moncur capped an impressive fightback with a second-half winner as Leyton Orient claimed a 2-1 League One comeback victory at Oxford to boost their play-off hopes.
The visitors had threatened in the first half with Cumming saving angled shots from Ruel Sotiriou and Moncur.
Tyler Goodrham fired the U's in front in the 20th minute, turning in Ruben Rodrigues' right-wing cross at the end of a fine move for his 10th goal of the season in all competitions.
Moncur was denied again before when Jamie Cumming parried his shot from 14 yards, while Tom James had a free-kick tipped over the crossbar.
Orient equalised six minutes into the second half when Ollie O'Neill shot - on the turn - low past Cumming from Idris El Mizouni's pass.
And Moncur completed the turnaround with a right-footed shot past Cumming from 16 yards after 77 minutes.
The result was no more than the Londoners deserved as they had enjoyed more possession and shots than the home side.
Orient boss Richie Wellens was sent to the stand for dissent in the closing minutes.