The Blues fought back strongly after the break. They scored four tries to the two of the Kings to take a 31-27 victory.
The Kings got on the board through Demetri Catrakilis with a penalty but it was Cardiff Blues who hit back with a try by Olly Robinson.
Demetri got a second penalty to take the lead again for the home side before Tienie Burger got over the line for the Kings.
The Blues who already got a yellow card early on received another one when their captain Nick Williams received a yellow card for a dangerous tackle.
This saw them playing with 13 men for a few minutes but they were able to hold the home side to the 13-5 lead going into halftime.
The visitors hit back immediately after the break with Liam Belcher crossing the tryline from a rolling maul.
The Kings came back at the Blues and Stefan Ungerer dived over the tryline to edge them back into an eight-point lead.
The Blues third try came from Matthew Morgan and Kristian Dacey got over not long after that.
It was then the Kings that had a player in the bin when Sexton was send off for collapsing a maul.
The Blues took advantage of this and Millard went over for the visitors in the corner.
Another yellow card was given to the Blues with the Kings this time taking advantage of the extra man to send Loubser over the line.
This was the last points in the match.
Southern Kings 27 (13) – Tries: Tienie Burger, Stefan Ungerer, Andell Loubser. Conversions: Demetri Catrakilis (3). Penalty goals: Catrakilis (2).
Cardiff Blues 31 (5) – Tries: Olly Robinson, Liam Belcher, Matthew Morgan, Kristian Dacey, Harri Millard. Conversions: Jarrod Evans (3).