Williams, who went into the game with 36 points to his name, from two games, crossed for a try and kicked 13 points via three penalties and two conversions.
The North must have fancied their chances before the interval when Jack Bennett (try) and Callum Phillips (conversion) put them into a decent position.
They trailed 10-7 at the interval but led 14-10 eight minutes after the break when Phillips converted his own try.
However, it was not enough to deny the hosts who struck twice through Daniel Thomas with Williams converting both.
It's now three games without a win for the North although their performance suggested that better times are ahead.
Blues South, who were 33-15 winners against Gogledd Cymru on Sunday, edged out the Dragons at Taffs Well thanks to tries from Lloyd Chalke and Tom Perry.
Gareth Thompson kicked 14 points in his side's 24-20 victory whilst for the visitors, Luke Morgan and Scott Matthews scored tries and Ethan Davies kicked two conversions. Niall Martin was also on the mark for the Dragons with two penalties, but his contribution came too late to save the game.
At under 18 level, Eli Walker and Bowdy Davies guided the Ospreys to a second successive victory of the season, against the Dragons at Newbridge.
Walker, who has been in outstanding form so far this season, produced another faultless performance, whilst Davies capped an excellent display with his first try of the season in a 28-16 victory at the Welfare Ground.
Walker was also on the try mark, with his his second of the campaign, whilst Luke Morgan bagged the third and Owain Williams kicked two conversions and as many penalties on top of a second half drop goal.
Trailing 20-9 to the interval, the Dragons struck back in the second half with a converted try from Matt O'Brien. However, it was not enough to deny the Ospreys a victory that keeps them on the coat-tails of early leaders the Blues.