Scrumhalf Piet van Zyl, who got a double last week, and winger Willie le Roux scored the other tries as a patient Cheetahs side emphasised their credentials and grabbed a bonus point with a strong second half performance after going into the break with a narrow 13-12 lead.
With both the Blues and Crusaders losing earlier in the weekend, the Cheetahs seized the chance to move up the table on the back of a dominant showing at the Nelson Mandela Bay Stadium, scoring their first try just before half-time and adding three more after the break.
Sadie’s first try came on the stroke of half-time as an accumulation of pressure allowed Le Roux to burst through a gap at pace and feed Sadie for the score.
Ten minutes after the restart a sniping break by Van Zyl added to the tally and was quickly followed by a second try for Sadie, who then turned provider to set up a well deserved try to Le Roux.
All four tries were converted by flyhalf Elgar Watts, who had also booted over two early penalties.
The Cheetahs have now won nine of their 13 matches and provisionally sit fourth on the overall table, with two matches in the round remaining.
It was another disappointing home defeat for the Southern Kings, who lie in 13th spot, who got a late consolation try through Argentine substitute Nicolas Vergallo with the last play of the match.
Flyhalf Demetri Catrakilis kicked over five penalties just days after being named in a Springbok training squad ahead of three June internationals.