Adam Chapman buried a late penalty under extreme pressure at the Kassam Stadium tonight to bring Oxford United a precious three points.

And that was after James Constable had missed from the spot at the end of the first half - on his return to the side.

Constable blazed his spot kick over the bar at the car park end, to continue what has been a poor run of penalties from United players.

But when Matt Green was fouled by James Stuart in the box with time running out, up stepped substitute Chapman in front of the home fans in the Oxford Mail Stand.

The former Sheffield United player hadn't featured much this season, and had only come on in the 69th minute because Dannie Bulman hobbled off injured.

But he kept his cool, and drove the kick straight and true into the net.

It enabled the U's to extend their lead at the top to three points over Stevenage, who were not playing.

Matt Green almost scored a second after a great run in injury time. Green did everything right on the run, but planted his shot over at the finish.

Fortunatey, it didn't matter.

In front of a big crowd, Oxford halted Rushden's four-match winning streak, but in truth it was an often disjointed performance, littered by mistakes, and sometimes strange decision-making.

All that will matter, though, is the three points, and United also had Ryan Clarke to thank for that.

He got right behind two firm shots by Mark Byrne at the end, and also made some key stops earlier.

The sides looked to be testing each other out in the early stages, without over-committing men forward, so it was a cagey beginning.

Nevertheless, Sam Deering poked a pass through to Constable, who got in behind Diamonds' defence only for keeper Dale Roberts, who was quickly off his line, to save with his body.

A clever backheel flick by Jack Midson wasn't read by Constable, but it was worth a try.

Constable, who regained the captain's armband on his return to the side, even though Chris Hargreaves was also in the team, was lining up in a 4-4-2 formation this time, with Midson alongside, and Sam Deering on the right of midfield.

There were few goalscoring opportunities at either end, and when one did come for Rushden, it tended to come from Oxford's own doing.

Rhys Day's weak header back to Ryan Clarke was pounced on by Lee Tomlin, but he produced a woefully tame shot, and Clarke saved with ease.

Damian Batt gave the ball away dangerously, in trying to preevent it going out for a throw, and the visitors broke with pace. Tomlin ran 40 yards, reverse-passed it to Aaron O'Connor to his left, but Clarke made a great smothering save.

Deering showed a bit of n aivety in going it alone and trying a difficult crossfield pass when Hargreaves looked to be better placed to make it.

And when there was a free-kick 30 yards out and wide on the left, almost the position from which Deering scored against Histon, the young midfielder tried the same thing, but this time it was straight into the keeper's grasp.

Constable managed a snapshot, after an intricate four-man move by the U's in a tight space, but it was straight at Roberts.

It was in the second minute of stoppage time at the end of the first half that United got the penalty, when Jake Wright was pulled back in the box by Jefferson Louis following a free-kick.

Louis protested his innocence and was booked, but Constable then blazed the penalty yards over the bar.

Louis was replaced for the second half with another ex-U's striker, Craig Farrell, taking his place.

Still there remained little between the teams, and once again United kept making problems for themselves by giving the ball away.

One corner by Deering, played short to Simon Clist, was immediately intercepted, and provided Diamonds with a break half the length of the pitch.

Wright body-checked Tomlin to prevent him bursting into the area, and was yellow-carded for his troubles, and Farrell fired the free-kick narrowly over.

Dannie Bulman hobbled off with a calf strain midway through the second half, and by then Matt Green had taken over from Midson.

Matt Green so often makes things happen. And he did it again.

Oxford Utd: Clarke 8*, Batt 6, Day 6, Wright 8, Tonkin 7, Deering 7 (F Green 90), Bulman 7 (Chapman 69, 8), Hargreaves 7, Clist 7, Midson 6 (M Green 63, 7), Constable 6. Subs not used: Turley, Creighton.

Booked: Wright, Batt.

Rushden & Diamonds: Roberts 7, Corcoran 7, Downer 6 (Osano 38, 8), Stuart 6, Robinson 6, Byrne 6, Wolleaston 8, Terry 6 (Porter 82), Tomlin 8, Louis 6 (Farrell h-t, 7), O'Connor 7. Subs not used: Day, Akurang, Booked: Louis, Stuart, Corcoran.

Referee: Steve Creighton (Berkshire) 6