The Giants threatened to cause an upset when they led 12-10 at half-time and the quarter-final tie was still in the balance until Grace – who this week extended his stay with the Super League champions to the end of 2022 – went over for his third try five minutes from the end.
The prolific Grace, who scored two tries in Saints’ victory over holders Leeds in the last round, now has 10 in seven league and cup matches so far this year and Wolf is confident he will stay with the club beyond his current deal.
He said: “I know Regan is really happy at the club and we’ll back ourselves, even though it’s a one-year deal, to make sure he will certainly stay long term.
“By his standards, he’s been really quiet the last couple of weeks, but tonight when he got the ball in his hands, we just knew he was going to score.
“I thought we saw a really mature performance from him, the way he went out and backed himself.
“When he’s in that frame of mind, you certainly want him in our team. He’s making lots of improvement and there’s plenty of improvement in him.”
Woolf was forced to shuffle his team after losing winger Tommy Makinson (foot) and prop Louie McCarthy-Scarsbrook (head) to injury early in the game, with hooker James Roby playing much of the game at loose forward.
Woolf said: “I’m really proud of the second-half effort. It’s hard to lose a winger in virtually the first carry of the game and then Louie had to go off.
“It meant some blokes had to carry more responsibility and play more minutes and that’s why I’m so proud.
“We had to think and adjust on the run and I thought Robes was outstanding tonight.”
Makinson had missed the previous two games with a foot injury but Woolf says he was fit to resume.
Woolf said: “It looks like he’s hurt his foot again. There is certainly no question about bringing him back too early. He trained fully for more than a week.
“But certainly there’s a bit of a drama and we will have to have a look at it.”