TOM Craddock's double was in vain as Oxford United paid for a slow start against Dagenham & Redbridge, who won despite playing the final 20 minutes with ten men.
The hosts were unusually flat right from the kick-off and there was little surprise when Sam Williams rewarded Dagenham's enterprise by heading in the opener.
It took Luke Howell's goal early in the second half to stir the U's, who quickly hit back through Craddock.
Luke Wilkinson made it 3-1, before Craddock's second restored hope.
United's attempts to salvage a point were boosted by Kevin Maher's 70th-minute dismissal, but a late Chris Lewington save from Adam Chapman sealed Dagenham's victory.
United's side showed two changes from the side which began Saturday's 2-0 win at Barnet.
Top scorer Craddock replaced Jon-Paul Pittman as expected, but Lee Cox came in for Alfie Potter, who dropped out of the squad with a hamstring
Johnny Mullins and Jake Forster-Caskey returned on the bench, along with Liam Davis, who was included in the squad for the first time this season after injury.
United had only played at home once in the previous month, but the Kassam Stadium was strangely quiet at kick-off.
The home fans had little to cheer in a first half which saw Chris Wilder's side lacking urgency and quality.
Dagenham seized the initiative and Medy Elito tested Ryan Clarke from range with their best early effort.
James Constable did his best to lift the mood, with two efforts on goal in the space of a minute.
The second chance was by far the best, running on to Craddock's through ball with only Chris Lewington to beat. The striker has been in good form, but his shot was too close to the goalkeeper, who blocked.
It was a rare bright moment for the U's, who clearly missed Potter's energy, and Dagenham remained the side who looked most likely to score.
Only a Jake Wright clearance off the line denied Dwight Gayle on 31 minutes, after Clarke had rushed out and failed to stop Williams' cross.
The inevitable finally happened five minutes later, when Williams rose to head in a Matthew Saunders corner.
A clever pass from Chapman presented Constable with another one-on-one late in the half, but again Lewington came out on top.
The game was transformed after the break by four goals in 11 minutes.
Howell doubled the Daggers' lead on 54 minutes, reacting first to fire home after Clarke parried Gayle's shot.
Craddock pulled a goal back on the hour with a brilliant cushioned volley after a lung-busting run and cross from Sean Rigg.
But within a minute United conceded at another corner, when Wilkinson was allowed a free header.
Then it was Dagenham's turn to shoot themselves in the foot. Femi Ilesanmi's awful back pass went straight to Craddock, who steadied himself before netting his 10th goal of the season.
The hectic spell continued when Kevin Maher received his second booking for a high tackle on Peter Leven.
It left United with a man advantage for the remaining 20 minutes.
The home side took some time to get to grips with the situation, but steadily increased the pressure on Dagenham's defence.
A quickly-taken free-kick gave Craddock a hat-trick chance, but he could only shoot over at full stretch from Constable's set-up.
Chapman thought he had equalised with a sweet left-footed shot from Davis' cross, but Lewington made an outstanding one-handed save.
It was the final clear chance as United's good recent run was brought to a halt.