JON-PAUL Pittman came off the bench to score the winner as Oxford United claimed a confidence-boosting win over in-form Northampton Town.

The striker's powerful finish was his first goal since January and ended United's four-game winless run.

James Constable's tap-in had given the hosts a lead at the end of a first half where Sean Rigg and Jake Forster-Caskey hit the woodwork.

But Northampton were always a threat and they drew level through Clive Platt's header.

Pittman quickly restored United's advantage and the Cobblers' chances of getting back into the game disappeared when Clarke Carlisle was sent off in the 89th minute.

Michael Raynes replaced the recalled Johnny Mullins at centre half in one of three changes from Tuesday's 2-2 draw at Barnet.

Lee Cox came in for Adam Chapman, while Jake Forster-Caskey started at the expense of Simon Heslop.

Alfie Potter reverted back to the right flank, so Rigg was pushed up alongside Constable.

The converted winger created the first chance on six minutes, when he charged down a clearance from a dawdling Lee Nicholls.

Constable got to the rebound first but he slipped, allowing the Cobblers goalkeeper to scramble the ball out for a throw-in.

Northampton arrived as npower League Two's form side and they looked dangerous on the break.

Former U's winger Chris Hackett provided their main outlet and had two early efforts.

An expectant crowd only had to wait until the 14th minute for the opening goal, scored by Constable.

The striker was unmarked to convert Potter's cross from six yards and although Northampton's players complained bitterly over an offside decision, the goal stood.

United came within a whisker of a second goal six minutes later.

Forster-Caskey won a free-kick out wide and from the set piece Peter Leven found Rigg, whose shot was deflected onto the crossbar.

Chris Wilder's side had hit the woodwork twice in stoppage time against Barnet and they were denied again just before the half hour.

Forster-Caskey was given space 20 yards out and the teenager let fly with a vicious, swerving shot which beat Nicholls but struck the post.

The rebound fell to Rigg, whose shot was turned behind by a relieved Nicholls, who saved from Andy Whing at the following corner.

Northampton may have looked unsteady at the back, but they remained dangerous at the other end.

A series of corners late in the half forced United to work overtime, but Ryan Clarke was in the right place to keep out a shot from Ben Harding.

Hackett fired the first opening of the second half wide, before Nicholls was called upon to make another good save.

Constable crossed low for Rigg, who turned in a flash and shot low, only to be denied by the goalkeeper's left hand.

Pittman had a great chance to score a minute after coming off the bench, but he missed the target from the edge of the box after good work by Potter.

Northampton brought on Platt to assist Adebayo Akinfenwa, who was being kept quiet by Raynes.

The visitors steadily increased the pressure, with Hackett fizzing a shot just wide, while Akinfenwa missed the target with a header from close range.

The momentum finally told 14 minutes from time, when Platt rose to head in Hackett's cross.

It was a blow to the hosts, but parity lasted for only three minutes as United struck back.

Leven launched a ball over the top which was perfect for Pittman, who steadied himself before lashing a shot past Nicholls.

The Cobblers threw everything forward in the closing stages in search of a second equaliser.

Hackett was again the most likely scorer and Clarke had to make one smart parry to keep one shot out.

Northampton's chances were dented a minute from time, when Carlisle collected a second booking for blocking off Potter.

United saw out the final minutes to claim a big three points.

Oxford Utd (4-4-2): Clarke, Whing, Raynes, Wright, Capaldi, Potter, Cox, Leven, Forster-Caskey (Pittman 56), Constable, Rigg (Worley 83).

Unused subs:Brown, Chapman, Heslop, O'Brien, Davis.

Northampton: Nicholls, Tozer, Carlisle, Langmead, East Robinson, Hornby, Harding, Demontagnac (Platt 61), Hackett, Akinfenwa.

Unused subs: Charles, Snedker, Mukendi, Moult, Huws.

Referee: Scott Mathieson.

Attendance: 6,635 (1,073 visitors).