Openers Reeza Hendricks and Gihahn Cloete then saw off the first eight overs of the reply to take the Knights to stumps on 19 without loss and make it the home side’s day.
The Cobras’ total was all the more disappointing for the fact that they had won the toss and elected to bat.
They found themselves struggling on 10 for three in the ninth over as Quinton Friend continued his excellent form, dismissing both Cobras openers in his first spell.
Ontong and Yaseen Vallie revived the innings with a 116-run partnership that gave the visitors a sense of parity, but Vallie’s dismissal for 50 sparked another collapse as Dane Vilas and Justin Kemp contributed just six runs each.
Robin Peterson’s 18 from 75 balls gave Ontong time to score some quick runs at the other end, but after he had fallen to stand-in captain Werner Coetsee (3 for 45), Friend returned to snaffle two more quick wickets and finish with figures of 4 for 25.
When the Cobras were bowled out, Ontong had contributed 57 per cent of their runs and just two other batsmen had scored more than the 12 extras.
Hendricks will resume on 13 not out on Friday morning, while Cloete is unbeaten on five.