The top five clubs all recorded victories in the seven Premier Division matches played on Wednesday evening.
Neath, Newport, Llanelli and Carmarthen Quins all won reasonably well, but fourth-placed Swansea had to go to the last seconds before winning 30-28 at Cross Keys. It required a Luke Richards touchline conversion for the two-point win - the last of his six successful goals.
Neath ran in six tries to defeat Llanharan 46-5 at the Gnoll with the visitors losing full back Marc Davies with a dislocated shoulder after scoring a try. Centre Andrew Bishop capped a fine evening with two tries and the man-of-the-match award.
Newport were held up by a 15-minute floodlight failure at Sardis Road, where Dan Griffiths kicked 13 points as last season's champions beat Pontypridd 23-7, while Jason Williams placed two penalties and converted a late Michael Scudamore try as Ebbw Vale defeated Bedwas 13-0.
Cardiff led 3-0 at Aberavon, but thereafter trailed the Wizards before going down 32-23 at the Talbot Athletic Ground. Wing Richard Carter, on permit from Neath, and skipper Dafydd Owen shared the four Aberavon tries while Elgan Jones notched his eighth and ninth for Cardiff.
Caerphilly were down by 32-0 after 40 minutes at home to Llanelli, but the visitors took their foot off the accelerator and coasted to a 35-17 after Caerphilly had run in three tries in the second period.
Carmarthen Quins defeated Bridgend by 28-7, including a 95th try of his league career from Quins centre Emyr Jones.
Llandovery meet Pontypool at Church Bank on Friday evening in a rearranged league match (7.15pm).
Carmarthen Athletic came from 3-0 down after 40 minutes to gain a 13-9 win at Kenfig Hill, where Bridgend Athletic had to take their home match.
Centre Chris Harries gained the only try of the match with Simon Morris and Lee Williams exchanging goal-kicks.