Oxford United lost for only the second time this season as Kidderminster stung them with a double blow early in the game.
Two goals in the first 17 minutes proved too big a task to come back from and in the end Oxford also lost a man, with left back Steve Kinniuburgh sent off for bringing down last player Matthew Barnes-Homer 14 minutes from time.
That brought Kidderminster a penalty and Robbie Matthews the chance to complete his hat-trick.
But Ryan Clarke brilliantly saved his penalty, to his right, and then produced an even better save from Brian Smikle's follow-up.
Sam Deering came in for his first start of the season for the U's, and he won a penalty which gave them some hope of recovery.
To add to Oxford's bad afternoon, striker Matt Green limped off with an ankle injury before the end.
United's legion of 2,000 supporters gave their team fantastic support when they emerged from the tunnel, totally drowning out any noise from the home crowd with their rendition of "Chris Wilder's Yellow Army".
But it was the worst possible start from the visitors as they fell behind in only the second minute.
Harriers began at a very fast tempo, and when a cross came in from the left, Luke Foster lost his footing as he went to intercept and the ball bounced up against his hand.
As the home fans yelled 'handball', Matthews didn't wait for a decision from any of the officials, simply firing the loose ball into the bottom right corner of Clarke's net before the keeper even had a chance to move.
The U's got back into the game, but with James Constable struggling, on his own, to get hold of the ball and keep it up front, Kidderminster were coming at them too often and too easily.
So when it became 2-0 in the 17th minute, Oxford's players knew they faced their stiffest test since they found themselves in a similar position at Mansfield.
Constable gave away a free-kick with a needless foul when chasing back, but it was still a wonder drive from Barnes-Homer.
The kick was played short, and Barnes-Homer hammered it from fully 30 yards past Clarke and into the goal for a spectacular strike.
Barnes-Homer it was whose excellent goal had brought Kidderminster victory over United in the corresponding league game last season.
United had begun the game with a 4-1-4-1 formation, Adam Murray deployed between defence and midfield, and Constable on his own up front, though with midfielders supporting whenever possible.
But it hadn't worked well, and at 2-0 down, Wilder reverted to two up front, Green moving up, and the midfielders altering positions to form more of a diamond.
Murray was booked for a foul on Duane Courtney but just before the half-hour mark, Oxford won a penalty and with it a real opportunity to salvage something from the match.
Steven Kinniburgh played the ball to Deering on the left edge of the penalty area, he reached the ball before goalkeeper Dean Coleman, who brought him down, and the ref pointed instantly to the spot.
Back on penalty duty, Constable calmly slotted it home, to Coleman's left as the keeper dived the other way, for his 12th goal of the season.
Deering was then not far away with a glancing header.
Mark Creighton joined Murray in the referee's notebook with what looked a very harsh yellow card after he simply challenged for an aerial ball.
From the free-kick, wide on the right, Danny Andrew drove in a shot that caught some of United's players by susprise, and came back off the chest of Ryan Clarke before he was able to gather at the second attempt.
Playing as the forward point of the diamond, Deering was finding space at will, and he embarked on one great run, freeing Dannie Bulman to his right for a shot which this time Coleman beat out, with some difficulty.
It was becoming end-to-end, and a cracking game of football, epitomised by Luke Foster having a header cleared off the line at one end, and then 20 seconds later Kidderminster almost scoring on the break at the other, Brian Smikle's shot well saved by Clarke.
Oxford finished the half strongly, but Kidderminster began the second one on top, and they made it 3-1 seven minutes after the restart.
Once again, United had allowed a cross to come in very easily, this time from Andrew on the left, and Matthews connected with a left-foot shot on the turn, the ball going under Clarke's body and in.
Jack Midson replaced Deering on the hour, and within moments he went on a run down the right that was ended only by a late challenge from Martin Riley, after he had crossed, that earned the Harriers defender a yellow card.
Oxford Utd: Clarke, Batt, Foster, Creighton, Kinniburgh, Murray (Kelly 68), Green (Chapman 83), Bulman, Clist, Deering (Midson 60), Constable. Subs not used: Turley, Day.
Referee: M Naylor (Sheffield).
Sent off: Kinniburgh.
Booked: Murray, Creighton, Constable, Green, Bulman.
Att: 3,569 (2,009 from Oxford).
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