Sydney Roosters surged to a 12-0 advantage before Cronulla responded in a semi-final disrupted by injuries to key players.
Nicho Hynes left the field within minutes after awkwardly positioning his head while attempting to stop Roosters second-rower Salesi Foketi.
Hynes was knocked down, and the Roosters immediately exploited the defensive lapse to score the opening points.
Showing Category 2 concussion symptoms, Hynes failed his assessment and missed most of the match.
Cronulla replaced him with Niwhai Puru straight away, indicating the Sharks had little expectation that their halfback would return.
If Cronulla progresses, the NRL's 11-day no-fault stand-down rule will prevent Hynes from playing in a possible preliminary final against the Dolphins next week.
The Sharks revived their hopes with tries in consecutive sets, reducing the margin to 12-10 with 15 minutes remaining before halftime.
Mawene Hiroti had left the field with a knee injury before those tries, although no diagnosis had been confirmed at publication.