Penarth slipped to only their second defeat in the Admiral League this season, going down 20-14 at Cambrian Welfare.
The Bears fell behind to two early tries from Jordan Roberts and Nico Watkins, before hitting back after the break with a brace from Will Odgers.
Despite going down to 13 men in the closing stages, Cambrian held out against the Division One East Central leaders, who remain four points clear at the top following St Albans' 35-27 win over Abercynon.
Cowbridge fell to a narrow 23-19 defeat at Wattstown in Division Two, while Llantwit Major earned the bragging rights - and a bonus point - over Dinas Powys in their Division Three derby, winning 30-17.
Old Penarthians were beaten 12-7 at Treherbert in Division Five and a depleted Sully Sports side were thrashed 78-0 by Beddau Athletic in their first home game of the Division Six campaign.
Next Saturday sees the last round of Admiral League fixtures before a month-long break for the Autumn internationals
Division One East Central
Penarth v Llanharan
St Albans v Barry
Division Two East Central
Cowbridge v Porth Harlequins
Division Three East Central
Llantrisant v Dinas Powys
Llantwit Major v Fairwater
Division Five East Central
Old Penarthians v Caerau Ely
Division Six East Central
St Peters Athletic v Sully Sports
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The draws have been made for the third round of the WRU's league cup competitions - with Penarth drawn at home to face Lampeter Town in Division One, while Cowbridge enter the Divsion Two Cup with a home tie against Usk.
Ties will be played on Saturday 6th December.
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