JORDAN Bowery had a debut to remember after the striker came off the bench to bag a priceless winner for Oxford United at promotion rivals Portsmouth.
He picked out the far corner with a superb 25-yard strike eight minutes after coming on, just a day after signing for the club.
It came 25 minutes after United blew a superb chance to open the scoring, when Liam Sercombe saw his penalty saved.
The visitors had to defend very well in two different periods during a tense second half to keep Portsmouth out, but held on to cement their position in the Sky Bet League Two automatic promotion places.
- Oxford United's 2,047 away fans celebrate after the final whistle
New signing Bowery was named among the substitutes as Danny Hylton was handed his first start for more than a month.
Callum O'Dowda also came into the XI as Michael Appleton made two enforced changes, with Ryan Taylor injured and Chris Maguire back at Rotherham United after his loan expired.
A packed Fratton Park ensured the game kicked off in a terrific atmosphere and the decibel level hardly dropped in a first half, despite the sides creating few clear chances.
United were quickly into their stride and saw plenty of the ball in their hosts' half.
Early corners led to Kemar Roofe heading over and George Baldock firing into the side netting.
Portsmouth handed a senior debut in goal to Ryan Fulton, signed on loan from Liverpool 24 hours earlier.
The 19-year-old had a big decision to make after a quarter of an hour, when Roofe's first-time pass sent Hylton through.
United's No 10 looked favourite to win the race, but Fulton sprinted out to clear the ball, avoiding what would have been a red card.
Unfortunately for the visitors, despite several promising moments going forward, the goalkeeper was otherwise untested before the break.
Defensively United were aggressive and had few nervous moments as Portsmouth often took a direct approach.
The exception came in the 19th minute, when superb one-touch football on the edge of the box presented a chance for Mark McNulty.
The striker's shot beat Sam Slocombe, but skipper Jake Wright was on hand to make a goal-saving clearance off the line.
United's best moment of the half came six minutes before the break.
Alex MacDonald did well to spot a burst forward by Sercombe, but the midfielder fizzed a shot wide instead of squaring for Hylton.
The midfielder had a chance to make amends five minutes into the second half, when Lundstram's prodded pass freed Hylton, who was brought down by Fulton.
Sercombe stepped up for the penalty, but saw both his initial spot-kick and the follow-up parried by the young goalkeeper.
It provided the home side with a big lift and they went on to enjoy a prolonged spell of pressure.
For almost ten minutes United barely had a kick - and when they did win the ball back all they could do was clear and give Portsmouth another chance to attack.
With the home fans cranking up the volume, the pressure grew.
United had to defend well, but Slocombe had nothing to do apart from claim a couple of corners.
Midway through the half Bowery was introduced, immediately giving the visitors strength up front.
Portsmouth were pushed back and United came again.
Hylton glanced a header just wide when he should have done better from a Roofe free-kick.
Bowery was waiting just behind the forward, but did not have long to wait before he lit the game up.
Running on to a raking pass from Wright, the tall striker came up with a brilliant low finish from 25 yards which found Fulton's far corner.
It came right in front of the massed ranks of travelling fans, who celebrated wildly before biting their nails furiously in a tense finale.
Portsmouth swarmed forward in the final quarter of an hour in search of an equaliser.
Twice Ben Close fired shots which fellow substitute Adam McGurk almost converted, but United held firm to claim a vital win.
Portsmouth: Fulton, Davies, Clarke, Webster, Stevens, Barton (Close 55), Doyle, Evans, Roberts (McGurk 63), Bennett, McNulty (Chaplin 82).
Unused subs: Jones, Burgess, Naismith, Tollitt.
Oxford Utd: Slocombe, Baldock, Mullins, Wright, Skarz, MacDonald (Bowery 68), Sercombe, Lundstram, O'Dowda (Evans 81), Roofe, Hylton (Hoban 88).
Unused subs: Buchel, Long, Dunkley, Ruffels.
Referee: Neil Swarbrick (Lancashire).
Attendance: 17,840 (2,047 visitors).
- Jordan Bowery and Jake Wright celebrate the winning goal