Right back Damian Batt was sent off as Oxford United's play-off hopes suffered a setback at Roots Hall tonight.

Southend became the first team to complete the double over them this season.

Two goals in quick succession just before half-time left the U's licking their wounds, after James Constable had fired them in front with his 13th goal of the season.

Batt was ordered off for a trip midway through the second half, a decision that looked harsh because it was a straight red card for effectively his first foul of the match.

There was just one change in United's starting line-up, with Simon Heslop returning to the midfield and Simon Clist dropping to the bench.

Also among the visitors' subs was new signing Simon Hackney.

The early exchanges were marked by a series of shots well off target, three by Southend, and one from United’s Asa Hall.

But in the 14th minute, it was precision personified as the U’s took the lead with a brilliantly-worked passing move from a free-kick.

Jake Wright played the free-kick, 30 yards out, short to Paul McLaren, and from his threaded pass, Harry Worley flicked it behind him and Constable, in space, took a touch and then drilled a low shot past keeper Rhys Evans and into the net.

That goal silenced the home supporters, and Oxford nearly doubled their lead two minutes later when Damian Batt delivered a trademark right-wing cross that Constable read, ghosting in unmarked, but he couldn’t get his effort on target.

The visitors went even closer to a second goal in the 22nd minute, from their first corner.

This time Constable saw his downward header bounce down and up against the bar. And when it came back, Hall, under pressure from two defenders, could not keep it down, and it cleared the crossbar.

The U’s were defending solidly, Harry Worley commanding in the air and Jake Wright putting Blair Sturrock under pressure as he shot, to ensure the effort flew over.

Having struck his first Oxford goal last week, Hall was getting in plenty of shooting positions again, and he was unlucky with one drive, that deflected off a defender and looped over the keeper, but just over the bar as well.

There was no warning of what was to come as United looked relatively untroubled at the back.

But Southend’s Ryan Hall punished Anthony Tonkin who skewed a clearance into his path. Hall controlled the ball with a great first touch, and then hit a half-volley low past Ryan Clarke to make it 1-1.

Suddenly Southend’s players had an extra spring in their step, and a little over two minutes later, just as the half entered stoppage time, the Blues struck again.

Peter Gilbert headed Hall’s left-wing corner against the bar, Clarke turning it onto the woodwork, and it dropped kindly for Bilel Mohsni, at the right post, to turn in.

The two goals must have left United shell-shocked as they trooped off at the interval.

Just 13 minutes into the second half, Clist came on for Asa Hall, and moments later Constable had a header saved from Tonkin's cross.

When Batt was dismissed, United's hopes of battling back all but disappeared.

Manager Chris Wilder had already brought on attacking subs to try to get back in the game.

So there had to be a reshuffle.

Tonkin went to centre back, and Worley moved to right back.

Several shots rained in from the home team, most of them over Clarke and over the bar.

Hackney showed his pace on one blistering run down the left, but at the end of it, Potter couldn't get a shot away.

Constable did later manage to send in a shot, swivelling with his back to goal and shooting with his trusty left foot, but it drifted wide.

Southend went above Oxford with this win. their third in a row, and next up for the U's is another difficult away game, at Gillingham on Saturday.