A 33-run Champions League Twenty20 triumph for the Knights was lit up by Williamson before the weather intervened in Raipur on Friday - he struck an unbeaten 101 from 49 deliveries as the New Zealanders totalled 206-5 in the first innings.
He was well supported by opening partner Anton Devcich, who made 67 in a first-wicket stand of 140 as the Knights consistently scored at more than 10 runs an over.
BJ Watling's 32 from 20 balls helped the Knights over the 200 mark, and the Cobras were well behind the rate at 44-2 from 7.2 overs when the rain fell to bring a premature end to proceedings.
Williamson and Devcich made a flying start, and were 51 without loss at the end of the six powerplay overs.
The duo continued to take the attack to the Cobras, bringing up the 100 partnership midway through the 11th over.
Devcich was eventually run out by a direct hit from Robin Peterson, but Williamson continued the onslaught and went to his century in style, crashing Vernon Philander over the cover boundary for six in the final over as the South African finished with figures of 2-39 from his four overs.
The Cobras' most impressive bowler was Charl Langeveldt, who recorded 2-27 from his allocation, but their reply got off to a nightmare start.
Trent Boult (1-8 from two) clean bowled Stiaan van Zyl very first ball, before Hashim Amla fell to the bowling of Scott Kuggeleijn, who took 1-11 from his solitary over.
With the Cobras still 33 runs short of the Duckworth-Lewis par score, the rain arrived and became increasingly heavy, meaning the Knights got their Group B campaign off to a winning start.