Williamson produced a sensational batting show as he remained not out on 101 to guide his side to a huge total at the Shaheed Veer Narayan Singh International Stadium here.
Incidentally, this was his highest T20 innings and first century in the shortest format. Today's total of the Knights was the first 200-plus innings of this edition.
Williamson hit eight fours and five sixes in his superlative 49-ball innings and his hundred came from just 48 balls.
Knights captain Daniel Flynn, however, did not contribute much as he was out for nought two balls after Devcich's dismissal.
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But Williamson continued his punishing mood as he made merry of a mediocre bowling and fielding display from the Cobras to steal the show.
B J Watling joined the party with a 20-ball cameo of 32 as he took 17 runs off Justin Kemp with a six and two fours in the 16th over.
For the Cobras, Charl Langeveldt and Vernon Philander took two wickets apiece while conceding 27 and 37 runs. Ll the Cobras bowlers, except for Langeveldt, were expensive with Justin Kemp conceding 34 runs from his two overs.