Oxford Harlequins were undone by a 17-minute period of madness in a 44-25 defeat at Old Patesians in South West 1.
Quins trailed just 16-11 after 51 minutes, but then pressed the self-destruct button and conceded four tries.
They did rally at the end with centre Nick Sevier scoring an outstanding try on his debut, but Quins will hope this performance was a blip.
The visitors were much changed from last season, and even from the squad they had named, but took the lead on 22 minutes through young wing Chris Williams after Charlie Mawle had kicked ahead.
Patesians No 8 James Pettigrew drove over for a try, which Adam Seager converted.
Sevier's penalty put Quins 8-7 up, but Mawle was sin-binned on 34 minutes and three Seager penalties gave Patesians a 16-8 half-time lead.
The second half saw Quins fly half Andy Noyce and home flanker Giles Potter yellow-carded for persistent off-side.
A second Sevier penalty narrowed the gap, but Henry Bird, Potter, Pettigrew and Ben Spry all crossed for Patesians with Seager converting three.
Sevier then ran in an individual score from 40 metres on 75 minutes, which he converted.
A minute later, an even more spectacular try followed for replacement wing Duncan Lynchsmith.
Full back Huw Jones started a fine team move, which went via four pairs of hands and set Lynchsmith on a diagonal run to the posts.
Sevier converted to completed a 15-point haul.
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