Wallingford ended Oxford's 100 per cent record in spectacular style with a 38-0 drubbing in Saturday's BB & O Premier Division contest.
Marshalled superbly by man-of-the-match Olli Henderson, the hosts racked up six tries, including two each for winger Nick Risk and prop Lee Blewett.
Blewett and No 8 Peter Thorns also had excellent games in what was comfortably Wallingford's best performance of the season.
The visitors, who were without eight players due to university commitments, are still ahead of Wallingford in the table, and could hardly have expected to last the season unbeaten.
But it was the manner of their defeat and second-half capitulation that will be of most concern.
A thrashing for either side looked a distant prospect in a dull first half-hour that produced few opportunities.
But Risk's 30th minute try, rounding off a slick backs move, opened the game up.
He should have scored two minutes before when he dropped Johnny Collett's after crossing the line, but Wallingford kept pressing and Risk made no mistake second time around.
With Dave Ralson punching holes in the home defence, Oxford would have settled for 5-0 at the break.
That margin became 12-0, however, when centre Don Jenkins fed skipper and fly half Henderson, who cut inside at pace, and scored under the posts before converting himself.
Two minutes into the second half it was 17-0 as Risk intercepted a stray pass and ran in from the 22.
Henderson converted again and maintained his form with two more points after Blewett smashed over in the 52nd-minute.
Oxford fly half Tom Olley missed a simple penalty before Blewett bagged his second try from close-range.
A quick line-out and a determined run from Jason Griffiths almost led to an Oxford score on 68 minutes.
Wallingford made it 38-0 with another converted try as Thorns picked up the ball from a five-metre scrum and sent scrum half Derek Viljoen over.
Oxford's shocker was completed with the sin-binning of scrum half Mike Clarke.
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