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Anthony Acheampong fired home an injury time winner as Welling moved up to fourth in National League South on Saturday.
The Wings looked to have thrown away two points before Acheampong got on the end of a knock down following a long free-kick to emphatically finish from inside the penalty area.
It was fitting that Acheampong scored the winner as he put in a man-of-the-match display at the heart of the Wings defence.
The defender headed wide from a Jack Jebb corner before Oxford took a 10th minute lead when Kabongo Tshimanga nipped in to round keeper Dan Wilks and slide home from an angle.
The woodwork denied Welling an equaliser when Jebb's free-kick caused chaos in the visiting defence before Acheampong was somehow denied from close range.
Welling deservedly drew level on 31 minutes when a period of pressure around the area ended with Jebb setting up Brendan Kiernan, who stroked home his fifth goal of the season from 20 yards.
The tireless Danny Mills, having lost the ball cheaply, then won it back from Udoka Godwin-Malife but could only pick out keeper Craig King with his cross.
Mills thought he'd scored his first goal for Welling four minutes from half-time but the linesman flagged was up for offside after he converted when King was unable to hold a long-range shot.
Oxford were much improved after the break and had enough chances to have wrapped the game up.
Wellings Thierry Audel missed a left-wing cross and it needed a cracking block by Craig Braham-Barrett to deny Tshimanga his second goal, Acheampong produced a brilliant block after Reece Fleet's forward run was not tracked, and then Kyran Wiltshire fired just wide of the upright.
Welling replaced the ineffective Bradley Goldberg and Gavin McCallum with Nassim L'Ghoul and Arnaud Mendy, allowing Jebb to play a more advanced role.
Acheampong shot weakly when a free-kick was not cleared before Welling went ahead on 71 minutes. Braham-Barrett, playing at right-back due to injury, delivered an inviting cross from the right and David Ijaha needed no second invitation to head home.
However, within three minutes Welling appeared to have pressed the self-destruct button as L'Ghoul's needless foul gave away a penalty, only for Patterson to blaze his spot-kick against the top of the crossbar.
Patterson did not miss his next opening, however, converting Ben Jefford's left-wing cross with eight minutes left to make it 2-2.
The visitors looked to have taken a decent point on the road but up popped Acheampong to make it back-to-back wins for Steve King's Welling team.
Welling: Wilks, Banya, Braham-Barrett, Ijaha (McDonald 89mins), Acheampong, Audel, Kiernan, Jebb, Mills, Goldberg (Mendy 65mins), McCallum (L'Ghoul 65mins). Subs not used: Ambroisini, Pinney.
Attendance: 465.