Three straight first-half tries and one of their best defensive displays of the season helped the visitors hold on at McDonald Jones Stadium and to 18 competition points on Saturday.
They had to dig deep late after an 18-6 advantage was trimmed to just 18-16 with 10 minutes to play via an 80m fumble return from Newcastle centre Bradman Best, but found a way to stifle the Knights and cling to victory.
But the massive injury for Keary has left the Roosters once again needing to shuffle their halves combination, the five-eighth leaving the game on 25 minutes with a suspected fractured jaw.
Keary copped an accidental boot from Dominic Young, as he made a defensive play on the winger who scored a try that was later pulled back on review.
It's the second jaw injury for Keary this year, having broken it in a pre-season training incident.
Bench utility Drew Hutchison moved into the halves in his absence to pair with Sandon Smith on his starting debut, the Roosters' most likely combination moving forward with Sam Walker sidelined due to a knee injury.
Joey Manu relished his move out of the halves and once again looked a complete natural at No.1, running for a whopping 295m and scoring a first-half try with perfect back-up play through the middle of the field.
They led 18-6 after falling behind early, their most impressive try Nat Butcher's equaliser off the back of a slicing run from Smith who looked more than capable in the halves.
Manu grabbed the lead soon after and winger Daniel Tupou extended it, capping a lengthy stand in Knights territory with some much-deserved points.
Young had opened the scoring thanks to a dynamic run from Kalyn Ponga, with the Knights fullback putting on a clinic to help his side back into the game in the second half.
Ponga put in another brilliant shift at No.1, running for 173m to go with seven tackle busts and a try assist.
Newcastle arguably did enough to win the game with five line breaks to three, with handling errors in key positions combined with a complete lack of red-zone creativity providing another blow to their chances of playing finals.
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