Marc Richards first half finish was all that separated Chesterfield and Oxford United at the Kassam Stadium.
A battling performance from the Spireites earned the visitors a crucial three points to keep their distant dreams of a League Two play-off spot alive.
A handful of crucial blocks from Liam Cooper and one outstanding save from Tommy Lee made sure of a double over Chris Wilder’s men - and a first win at Oxford since 1980.
Drew Talbot returned from an illness that kept him out of the 2-0 defeat of Bristol Rovers last week for a place on the bench, while striker Richards was recalled to first team duties.
Tendayi Darikwa, fully recovered from a hernia injury, made his first start for the club since the draw at Rochdale on February 2.
And, with barely five minutes on the clock, the visitors struck with their first attack of the game.
Richard Brindley slotted an inch-perfect ball through to Richards, who wriggled free of his marker and lifted the ball over the onrushing Luke McCormick from 12 yards.
The Spireites settled quickly but were given a warning of Oxford’s attacking menace when top scorer James Constable got to the byline and pulled a ball back to Alfie Potter whose shot was promptly charged down.
Lee uncharacteristically fumbled a high ball into the box and was fortunate Sam Togwell was on hand to clear the danger.
While at the other end, a dangerous free kick from Conor Townsend was well punched clear by McCormick under pressure from Neal Trotman with the defender coming off worse.
Cooper had to hack the ball off the line to preserve Chesterfield’s lead from Deane Smalley midway through the first half. The former Spireite looked certain to equalise from six yards but was bravely challenged by Nathan Smith, who was clearly hurt from the collision.
Moments later the left back then went down near the touchline only to be hoisted off the pitch by Smalley, who was subsequently booked to the annoyance of the home support.
Smith was replaced by Danny Whitaker, with Townsend slotting in at the back four.
The youngster, on loan from Hull City, came inches away from making it two with a curling free kick that nestled on the roof of the net.
Back came Oxford with Potter and Scott Davies both having shots blocked before Lee spread himself to deny Constable on the stroke of half time.
Smalley’s shot from an acute angle was plucked out of the air by Lee early in the second half before the Spireites came close to doubling their lead.
A flowing move from right to left gave Jay O’Shea the chance to run at the Oxford defence, which he duly obliged. The frontman danced around a handful of challenges before curling an effort fractionally wide of McCormick’s right hand post.
Richards, who was a thorn in Oxford’s defence all afternoon, had a penalty claim turned down after a tangle with Jake Wright.
Whitaker had the ball in the back of the net only for a linesman’s flag to cut the visitor’s celebrations short as Chesterfield continue to look dangerous on the break.
Substitute Tom Craddock showed his keen eye for goal, testing Lee down at his near post from an inside left position, before clearing the crossbar with a clear sight of the posts from 12 yards.
O’Shea then showed more neat footwork to pirouette his way past two tackles but his cross to the back post was just to high for Richards, who would have had the simple task of nodding into an empty net.
Cooper made another crucial block to deny Craddock from the edge of the area as the hosts tried desperately to force an equaliser, which ultimately never came.
Spireites (4-4-1-1): Lee; Brindley (Randall 89), Smith (Whitaker 30), Cooper, Trotman; Togwell, Hird (c); Darikwa (Talbot 70), O’Shea, Townsend; Richards
Subs not used: Barrington, Clark, Henshaw, Lester
Oxford (4-4-2): McCormick; Batt, Raynes (Worley 88), Wright (c), L.Davis; Potter, Rigg (Craddock 65), Whing, Davies; Smalley (Parker 81), Constable
Subs not used: Duberry, Heslop, Brown, O’Brien
Referee: Darren Bond
Bookings: Smalley 29, Worley 90+2;
Attendance: 6,003 (385)