Ritchie Humphreys' first-half volley proved to be enough to give Paul Cook's unbeaten side all three points, with Andy Whing's dismissal effectively ending Oxford's hopes.
Fleetwood Town sit in second place following their 1-0 triumph at Portsmouth, a Sonny Bradley own goal giving the visitors the points as the unfortunate defender deflected Jamille Matt's strike into his own net.
AFC Wimbledon capitalised on Oxford's loss as they moved into third with a 3-1 victory over Burton Albion.
Burton took the lead through attacker Adam McGurk, despite being reduced to 10 men when Marcus Holness was sent-off, but goals from Harry Pell, Jack Midson and Andy Frampton ensured success for Wimbledon.
Mansfield Town eased to a comfortable 3-0 win over Northampton Town, attacker Ben Hutchinson and midfielder Sam Clucas scoring in the first half, before an own goal from Mathias Kouo-Doumbe put the gloss on a fine performance.
York City ended a run of four consecutive defeats with a 1-1 draw at Wycombe Wanderers, Dave McGurk putting Nigel Worthington's men in front with a header after 64 minutes, only for Dean Morgan to level six minutes later with his fifth of the season.
Goals from Matthew Lund and Scott Hogan gave Rochdale a 2-1 win at winless Accrington Stanley, who failed to capitalise on the dismissal of George Donnelly after Kayode Odejayi had pulled one back.
Torquay United won a six-goal thriller with Cheltenham Town, triumphing 4-2.
Callum Ball scored twice in the first half for Alan Knill's men, with Karl Hawley and Jordan Chapell putting the game beyond doubt in the second half, despite goals from Byron Harrison and Terry Gornell for the visitors.
Dagenham and Redbridge drew 2-2 at Morecambe thanks to a 94th-minute goal from striker Rhys Murphy, who found the net from close range after Padraig Amond and Mark Hughes had turned things around for the hosts following Abo Ogogo's opener.
John-Joe O'Toole earned a 2-2 draw for Bristol Rovers against Hartlepool United, the midfielder levelling matters late on after Hartlepool had cancelled out Matt Harrold’s opener with a double from Luke James.
Elsewhere, Scunthorpe United beat Plymouth Argyle 1-0, Newport County won 2-0 at Exeter City, and Bury drew 1-1 with Southend United.
