Chippenham were left pondering missed opportunities as Maidenhead snatched a 22-19 victory in South West Two East.
The Wiltshire side took an early lead at Braywick Park, thanks to a James Barnard penalty, but Maidenhead went over for their first try soon afterwards.
The conversion was added before Chippenham hit back with another Barnard penalty.
Although Trewartha added a try and Barnard the conversion, numerous scoring chances were missed.
An injury to Trevor Lloyd also unsettled the team for a while as Nick Fitzwater replaced him at fly-half.
Maidenhead took advantage and after 30 minutes they managed to scramble over from a catch and drive at a line-out.
But Barnard converted another successful penalty, giving the visitors a slender lead at half-time.
Chippenham moved into a 19-14 advantage thanks to yet another Barnard penalty, but it didn't last.
From a penalty midway inside the Chippenham half, Maidenhead kicked to the corner and again used the rolling maul to push over for their third try.
The conversion was missed, but Maidenhead added their first penalty to clinch the win.
Chippenham: Pratt, Spence, Newson, Todd (replaced by Watkins) Thornton, McNerlin, Cooper, Sherratt, Dunford, Lloyd (replaced by Fitzwater), Smith (replaced by G Squires), Crockett (Captain), Spurway, Trewartha, Barnard
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