If Oxford United supporters had any doubt that they have a team with genuine promotion hopes, they don’t now.

While there was plenty of doom and gloom following Saturday’s defeat at Rotherham in their opening league match, Wednesday's terrific effort in round one of the Carling Cup against Championship side Cardiff certainly saw expectation levels rise.

Yes, the Welsh side had players missing. And yes, Oxford lost. But the scoreline really flattered the visitors – as the standing ovation at the final whistle showed.

United will feel aggrieved to have trailed in the 12th minute.

The visitors had hardly been in the U’s half when Jake Wright attempted to cut out Jon Parkin’s centre. The ball fell for Craig Conway, whose cross deflected off Wright and Damian Batt was not able to stop the ball crossing the line.

United drew level on the half-hour when Simon Clist’s through ball was dummied by James Constable and Jon-Paul Pittman raced through one-on-one with Tom Heaton.

His finish was poor, but the save off the keeper’s legs found Clist on the edge of the box and his left-foot shot, with the help of a slight deflection, found the net.

After neither side could find a winner in normal time, Peter Whittingham latched onto a free-kick, and with no-one man closing him down, fired past Clarke from 20 yards.

Asa Hall hit the bar as Oxford tried all-out for an equaliser, but their attempts proved in vain.

Boss Chris Wilder made three changes from the side that lost to Rotherham and reverted to his 4-3-3 formation.

Alfie Potter and Pittman were promoted from the bench to partner Constable in attack, with Clist coming in for Anthony Tonkin.

Clist occupied the left side of midfield, with Liam Davis reverting to left back.

Cardiff, who had nine players on international duty, made nine changes from the side that beat West Ham in the Championship on Sunday.

The two sets of fans exchanged pleasantries – Cardiff informing Oxford that they only had three stands, and the U’s responding by reminding the Welsh following that Swansea were in the Premier League.

It was all good humour.

Having fallen behind to a goal from the first Cardiff attack, Wilder’s men regained their composure and started to knock the ball around well.

It was from some precise passing that they found the equaliser on the half-hour mark, and for the remainder of the half, they were on top.

Cardiff began the second half better, but Oxford soon went through the gears.

The frustrating thing from their point of view was that again delivery from set-pieces was extremely poor.

It was only when Peter Leven came on that the visiting defenders were put under pressure by balls into the box.

The U’s had a big penalty shout when Constable’s shot was blocked by Gabor Gyepes, and trying to get to the rebound was caught by the defender.

Leven, who had come on along with loan signing Lewis Guy, impressed, and from his ball in, Michael Duberry headed over.

Duberry and Parkin were booked after a clash, the yellow for the U’s man unjustified.

Clarke then made a superb save from a Gyepes header, and reacted well when Ibrahim Farah tried to turn the ball in from a yard out.

Eventually United's defence hacked the ball clear.

In injury time, Leven’s inch-perfect pass set Guy free, but his attempted lob was poor and Heaton saved. It was a golden chance.

There was controversy in injury time when a Cardiff man was down and United were playing the ball out of play, only for the visitors to intercept and race forward and win a corner.

Opposing manager Malky Mackay told his side to give the ball back, but they didn’t.

In extra time, Whittingham’s goal knocked some of the stuffing out of United.

But they kept coming forward, with Hall’s header against the bar from Leven’s free-kick the closest they came, despite playing Duberry as an extra striker for most of the second period.

And to rub salt into the wound, Jarvis latched onto a long ball to head over Clarke and into the empty net to put the final nail in United’s coffin.

Oxford Utd: Clarke 7; Batt 7, Duberry 8, Wright 7, Davis 8; Hall 7, Whing 7, Clist 7 (Leven 62, 8); Potter 8 (Smalley 91, 7), Constable 7, Pittman 7 (Guy 62, 6). Subs not used: Heslop, Payne, Brown, Worley. Booked: Duberry.

Cardiff: Heaton 7; Quinn 7, Evans 7, Gyepes 7, Naylor 6; Conway 7, Taiwo inj (Whittingham 16, 8), Farah 7, Taylor 7 (Ralls 67, 6); Parkin 7, Gestede 6 (Jarvis 6). Subs not used: Marshall, Hudson, Gerrard, Oshilaja. Booked: Parkin, Farah, Jarvis.

Attendance: 5,435 (780 from Cardiff).

Referee: Andy D'Urso