Lloyd banged over six goals in atrocious conditions at the Groe as the Bulls shrugged off an early 19-0 deficit to beat the table-toppers 26-22. Forwards Ben Duggan and Gareth Kinsey scored second-half tries for the home side.
Team manager Justin Lewis said the victory was perfect preparation for his side's Konica Minolta Cup quarter-final match at Pontypridd next Saturday.
"We were 19-0 down after only 10 minutes, but we had chosen to play into the wind in the first half and that paid off," he said.
"It wasn't a day for the backs, so in the second half, we knew we had to keep it in the forwards and keep driving it up the middle. We've missed Rob Lloyd for the last three games, because he's a Marine and he's been away, and his kicking was crucial.
"We said before the game that we could win this one, and we knew it would give us a lot of confidence ahead of playing a Premiership side at Sardis Road.
"This season is strange - we can produce this sort of performance against the good sides, but can't seem to do it against the poorer sides."
Despite the loss, Bonymaen are still warm favourites to finish on top of the league. Their nearest rivals, Beddau, had a royal chance to narrow the margin to two points but crashed 31-13 at home to fellow title contenders Newbridge.
In another game decided by the wind, Beddau led 13-11 at the break, only to concede second-half tries to forwards Chris James and Chris Payne. Newbridge outside-half Greg Jones added 16 points with the boot.
Cwmllynfell continued their fine season with a 23-15 win at Caerphilly, with Neil Thomas, Paul Davies and Jim Morgan scoring tries for the visitors, while Merthyr ran in five first-half tries in their 27-10 victory over Narberth.
Waunarlwydd shut out Fleur de Lys 15-0, with a try double to Ed Bennett, and Blackwood found their feet in the second half to come back and beat Llanharan 20-15.
Fourth-placed Whitland spurned a chance to climb the table when their home match against bottom-placed Ystrad Rhondda finished in a rare nil-all draw. The mid-table Llangennech-UWIC match was abandoned at halftime because of torrential rain. Llangennech were leading 7-5 at the time.
A special video package as Pontypridd claimed the double for the first time in their history by winning the Principality Premiership final, including match build-up, highlights, post match reaction and dressing room celebrations.