Werner Coetsee's five wickets were the catalyst for the Knights to spring a surprise two-wicket victory over the table-topping Cape Cobras at Newlands.
Resuming their second innings on 74 for two, the hosts were bowled out for 209 after half-centuries from Andrew Puttick (55) and Yaseen Vallie (68).
Spinner Coetsee bagged five for 34 to leave the visitors needing 170 for victory.
The Free Staters then set about their run chase smoothly by reaching 75 for one but 4/60 from Dane Piedt and 3/29 by the competition's top wicket-taker Beuran Hendricks ensured there was a nervy finish.
Pite van Biljon's 44 was the top score for the Knights as they claimed a prized win over the defending champions and one which enabled them to end the first part of the campaign in the number one position. – Sapa