Birmingham gave their outside play-off hopes a boost with a 2-0 victory over strugglers Oxford at the Kassam Stadium for their fourth away win of the season.
A goal midway through each half inflicted a first defeat on Matt Bloomfield in his fourth game since taking charge at Oxford.
Blues took the lead in the 23rd minute through an own goal by Myles Peart-Harris, who headed Jamie Cumming's flapped clearance at a Paik Seung-ho free-kick into his own net from five yards.
Marvin Ducksch made it two in the 67th minute with a clinical right-footed finish from 22 yards, after substitute Carlos Vicente's backheel, for his seventh goal of the season.
It was Spaniard Vicente's debut for Birmingham, the winger having only signed from Alaves in the week.
Despite winning League One with a record number of points, City had won only three away games in the Championship coming into this fixture, and were clearly intent on improving that mediocre form in what was their first visit to Oxford in the league this century.
United, their confidence high after winning at Leicester, started the game well with Peart-Harris finding room down the right wing, and in the opening seconds managed an effort on goal, Matt Phillips controlling the ball on his chest but then shooting wide.
After another attack down the right and good play by Stan Mills, Peart-Harris then scuffed a 22-yard shot wide moments later.
It was slightly against the run of play when Blues took the lead midway through the first half from Peart-Harris' own goal.
The free-kick which led to the breakthrough came when Brodie Spencer needlessly fouled Ibrahim Osman near the by-line, earning him a yellow card.
The goal dented the home team's confidence and led to a spell of Birmingham possession and pressure, which resulted in two goalbound shots blocked before captain Christop Klarer headed over the bar in the 37th minute.
Oxford responded before the break with Cameron Brannagan having a deflected shot from outside the box saved by James Beadle.
Just after the restart, City almost doubled their lead. Jay Stansfield's right-wing cross was met by Osman, coming in fast, at the far post but he knocked the ball the wrong side of the post before skidding through and becoming entangled in the goal netting.
The second goal killed from Ducksch off Oxford's hopes, though they nearly pulled one back after 87 minutes when Beadle saved from substitute Ole Romeny after a quickly taken throw-in.
Only a fine save by Cumming at his near post prevented August Priske from making it three for the visitors in stoppage time.
Oxford's Matt Bloomfield:
"Brodie Spencer just mistimed his tackle and has given away a foul in the corner, and they've moved the ball and taken it from a better angle to have almost like a shot - and that was quite decisive because where the foul was it should have been in the corner.
"I'm a little bit annoyed with that because those moments make a big difference to the end result.
"It had a big bearing on the game but after that we have to make sure we react better. It knocked the stuffing out of us a bit because until then our shape had been really good.
"First defeat and don't like losing - hate it. But we need to move on quickly and look forward now to Tuesday evening (at Sheffield United).
"It's going to be a roller-coaster between now and the end of the season. The last week has typified that."
Birmingham's Chris Davies:
"I was pleased with the result obviously but also very pleased with the performance.
"We've been working on controlling games and the way that we got control and worked the ball, and had the calmness to play around and switch the play rather than just go forward early and maybe lose the ball, was great.
"That level of control worked them hard and took away from them a little bit. I liked the way that we played that match.
"You get battling performances where you smash and grab, but this was a professional away performance where we knew what we were doing and deserved the win.
"We looked solid and aggressive without the ball, and then with the ball there was a composure and a control - and that's when we're at our best."
