Their 74-7 annihilation of bottom-of-the-table Neath enabled them to cut the gap at the top behind Merthyr to seven points.
The Ironmen host RGC 1404 at The Wern on Saturday kmowing that if they win they will make it a hat-trick of titles.
Neath had the temerity to take the lead in their final game of the season, James Roberts crossing for the shock score and Jordan Rees adding the extras, but after that it was one-way traffic as WRU National Cup winners Cardiff ran in five tries to lead 33-7 at the break. They then added a magnificent seven more in the second half.
Leading the home charge was full back Edd Howley, who claimed a hat-trick, while No 8 Aled Cockwell, man of the match against Ebbw Vale, scored a try in each half.
Other tries came from Morgan Griffiths (2), Matt Powell, Joe Gatt, Ina Jenkins, Llywarch ap Myrddin and James Murphy. Gareth Thompson kicked added seven conversions.
Another of the relegated sides, Cross Keys, forced another of the top teams, Pontypridd, to work much harder for their bonus point.
It was only 7-0 to the visitors at half time at Pandy Park hanks to a try from Alex Webber, converted by Ceri Sweeney, and then the home side hit back with a try of their own.
The experience of former Wales outside half Sweeney then came to the fore as he kept Ponty, still in with an outside chance of taking the title, moving forward in pursuit of the three more tries they needed to take the five points.
He converted a 58th minute Dale Stuckey score, crossed for a try himself 10 minutes later, and then saw Gabe Davies bring up the bonus point with the fourth try on 72 minutes to make it 24-5.
Swansea ended their season on a high with a 24-14 home win over Aberavon to end a run of back-to-back defeats.
The Whites had to hit back from a 7-3 interval deficit and the game didn’t go the way of Aberavon scrum-half David Pritchard on his 250th appearance.
Swansea scored three second half tries through Ifan Phillips, Gareth Rees and Thomas Williams, while Steff Williams converted all three and kicked a first-half penalty.
Principality Premiership results – Wednesday May 8
Cardiff 74-7 Neath
Cross Keys 5-24 Pontypridd
Swansea 24-14 Aberavon
