The previous weekend the west Wales side had been 29 points clear at Aberavon before ending with only a share of the pints in a 32-32 draw.
But this time they squandered a 21 point advantage shortly after the break at Parc y Scarlets before not only conceding victory to Neath, but also a try bonus.
The yellow card received by lock Adam Powell 15 minutes into the second half proved crucial and the visitors ran in two tries before striking through Kevin James for the vital, match winning fourth.
The five point raid in the west by Neath means they move up the table into second, just three points behind league leaders Pontypridd. Paul John’s Sardis Road outfit knew they had to win against Cardiff to stay on top and the boot of outside half Dean Gunter did the damage for them.
He kicked four penalties in the first half and another after the break to secure victory. Wing Owen Williams grabbed the visitor’s only try, while Rhys Shellard and Matthew Veater crossed for the home side.
Both teams had a player sent to the sin bin and the game ended with passive scrums after Cardiff suffered front row injuries.
Swansea sailed into a 20-0 interval lead at Glamorgan Wanderers before eventually grabbing a try bonus in a 28-12 triumph. With a game in hand on the Pontypridd and Neath, they could climb back to the top when they make up their fixtures.
David Watts, Leigh Bevan, Luke Jones and Rhodri Wells crossed for the visitors and James Dixon kicked two penalties and a conversion. The home side nabbed two tries in the final five minutes to add some respectability to the scoreline, Charlie Johnson and Dan Fish getting the scores.
Premiership new boys Carmarthen Quins took a giant step away from the relegation zone as they ran winless Pontypool ragged to pick up a bonus point in a 40-10 away win. Scarlets wing Darren Daniel enjoyed his visit to Pontypool Park as he zipped over for a hat trick of tries.
Richard Carter and Ellis Lloyd scored the other two tries for the visitors and Gareth Cull added 15 points with the boot. Steve Taylor scored Pontypool’s sole try and, to make matters worse, they had No 8 Sam Pailor sent off for punching.
Ebbw Vale must have been thinking about notching a second win when they went into the interval at home against Llandovery 16-10 in front. But in the end the Steelmen fell to a disappointing 24-22. Gareth Bowen kicked 17 points for the home side, but two tries from Wales Sevens wing Ifan Evans, and a third from centre Joe Ajuna, secured the points for the visitors.
A late Dan Davies try earned Aberavon a bonus point at home against Newport, but they conceded three in a 27-20 defeat. Cross Keys had tries from Rob Nash and Will Johnson to thank for their 20-13 home triumph over Bedwas.
