Oxford Harlequins recorded their first victory at Bicester since their formation in 1996 when they edged home 17-13 in a tight contest.
Bicester, hampered by early injuries to winger Chris Austin and scrum half Chris Nash took the lead after seven minutes from a line out on the Quins line.
Mark Malins caught cleanly, and the pack drove hooker Martin Ewins over for a try.
Paul Browne slotted a penalty for Quins, but, from another line-out after 25 minutes, Malins this time detached himself from the maul to go over for a try to make it 10-3.
Five minutes later, Quins were back in the game.
Eighteen-year-old fly half Henry Pooler outstripped the home defence in the chase for Steve Chadbone's kick-ahead, gathered and touched down for a try.
Browne missed the conversion, but then landed a fine penalty to give the visitors an 11-10 interval lead.
Playing into the wind and rain, Quins marshalled their defence superbly in the second half, with scrum half Nick Walker having an outstanding game.
Two well-struck penalties by Browne extended Quins' lead to 17-10, before Dafydd Gould replied in kind for Bicester.
Grove kept up their promotion hopes with a 25-12 victory at home to Bletchley.
Tries by centre Ben Dean and flanker Ben Nicholl gave Grove a 10-5 interval lead, before Bletchley's big pack got on top in the early stages of the second half.
Grove started to move the ball wide, and the tactic reaped dividends with further tries by winger Chaz Boshell and lock Dean Fielder his first of the season.
With Dean Hammett converting a penalty, Grove had a commanding lead and so were unperturbed when Bletchley fought back with a late converted try.
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