Eben Botha (21* off eight balls) and Wesley Marshall (20* off seven) had climbed into the Knights bowlers before the covers came on for the last time.
With no reserve day scheduled, the no-result means the Knights progress to Friday’s final against the Dolphins on overall net run rate.
Earlier, the Free Staters posted 127-7 in their rain-reduced 19 overs, with Pite van Biljon scoring 29 off 24 balls and Gerald Coetzee 29* off 12.
Eldred Hawken took 3-37 and Senuran Muthusamy 2-12 for the Dragons.
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