League Two leaders Chesterfield earned their seventh win in eight games with a narrow victory at 10-man Oxford.
Ritchie Humphreys volleyed in Eoin Doyle's cross to put the Spireites ahead on the half-hour mark.
Oxford defender Andy Whing was shown a straight red for a sliding tackle on Doyle midway through the second-half.
Ryan Clarke made a string of fine saves as Chesterfield dominated, but Dean Smalley almost equalised five minutes from time when his header hit the post.
The win for Chesterfield maintained their four-point lead at the top of the division, while Oxford's first defeat of the season saw them drop out of the top three.
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Chesterfield goalkeeping coach Eric Nixon told BBC Radio Sheffield:
"It was a hard-working performance, but I feel on the day it could have been more goals for us.
"Obviously Oxford are a really good side, but it's nice to come and get three points.
"We've got a great system and the football we play is pleasing on the eye."
Oxford United 01 Clarke 03 Newey 04 Raynes (Davies - 72' ) 13 Hunt 19 Mullins 10 Smalley 14 Hall (Rigg - 53' ) 16 Whing Dismissed 17 Rose (Ruffles - 90' ) 08 Kitson Booked 11 Potter Substitutes 25 Jalal 18 Davies 34 Bevans 15 Williams 33 Shama 07 Rigg 37 Ruffles Chesterfield 01 Lee 04 Hird Booked 06 Cooper 15 Humphreys 25 Talbot 05 Morsy Booked 07 Darikwa (McSheffrey - 71' ) 10 O'Shea (Devitt - 90' ) 11 Roberts 12 Ryan 17 Doyle (Gnanduillet - 83' ) Substitutes 20 Chapman 08 Togwell 23 Evatt 27 Edwards 16 Devitt 21 Gnanduillet 28 McSheffrey