Hynes was phenomenal in last week's 66-0 thrashing of the Dolphins, scoring two tries and setting up three others.
With 30 points for the game, the Sharks halfback set a new record for most points by a Cronulla player in a match.
The 30-year-old's hot-and-cold form, and record in pressure games, has made him a lightning rod for criticism since his 2022 Dally M Medal-winning season.
But Hynes appears more comfortable than ever next to halves partner Braydon Trindall as the fourth-placed Sharks eye another deep run in finals.
"Most halves are under more pressure than the rest of the team because they're tasked with the delivery of getting a team over the line," Fitzgibbon said.
"If your team's close and you don't tend to win, they tend to be under more pressure than anyone else, and none more so than Nicho."
Fitzgibbon has seen growth in Hynes over his five seasons as coach.
"(Hynes) handles it a lot better nowadays," Fitzgibbon said.
"He's a pretty strong-minded guy and is playing some good footy. We're really comfortable with the way him and 'Tricky' (Trindall) are developing together."
Fitzgibbon said it would be a "challenge" to back up such a dominant performance as the road win over the Dolphins.
"It's a rare day, not everything goes your way like that usually," he said.
Cronulla have a chance to send another warning shot to premiership rivals, hosting fifth-placed Newcastle on Friday night.
"They've been entrenched up the top of the ladder for nearly the whole season. They've got class across the board there," Fitzgibbon said.
"We'll have to be strong in all areas."
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