Despite taking an early lead with a Theo Fages try, Saints were on the back foot for most of the first half as Castleford established a 12-6 lead courtesy of converted tries from Niall Evalds and Jake Trueman.
Woolf was forced to change his team for the second half, with Fages unable to continue due to a shoulder injury, and he was grateful for the contribution of his replacement Jack Welsby as they went on to score 20 points without reply to win 26-12.
"We needed half-time actually," Woolf said. "Their first try really rattled us and we began making a lot of errors.
"We were all over the place, a bit jumpy on the edges. We were not quite where we usually are.
"I thought the period just before half-time was crucial. If they had scored another try, it would have made it really tough for us.
"To come out and score the first try of the second half was really big."
Woolf revealed it was Fages who took the decision to keep himself out of the action for the second half.
"I can't praise him enough," Woolf said. "He had the problem really early in the piece but he's a tough little bugger and he tried to battle on.
"A couple of times he went to throw a pass and had no power. He made the decision at half-time because he felt he was letting the team down.
"Thankfully we had Jack Welsby on the bench and he did an outstanding job."
In adding the Challenge Cup to their Super League trophy, Woolf has topped the achievement of his predecessor Justin Holbrook while captain James Roby collected a fourth winners' medal and was among the second-half tryscorers, 14 years after scoring the first try at the renovated stadium.
Woolf said of the veteran hooker: "He was outstanding. To be doing what he does at his age is outstanding, he doesn't look like he is slowing down at all."
The consolation for Castleford was the awarding of the Lance Todd Trophy as man of the match to full-back Evalds, who was on the losing Salford side in 2020.
"That shows how well we attacked at times," Tigers coach Daryl Powell said. "We got Niall away a few times but they take some breaking down."
A second Wembley defeat in eight years has denied Warrington-bound Powell the chance of bowing out of in charge of his hometown club with a major trophy and he could not hide his disappointment.
"I thought we started both halves really poor," he said. "Going six points up and giving it up so quickly at the start of the second half had a big part to play.
"They clearly stepped it up and we didn't handle that. It could have gone either way but they defended phenomenally well and we lacked composure.
"I'm super proud of the players, they had a real go today. It didn't quite happen in the end, we weren't quite good enough in the second half, but I don't think that scoreline reflected the game."
Powell had no complaints over the controversial nature of Roby's try, awarded despite the suspicion of a knock-on and a potential foot in touch by winger Regan Grace.
"I initially thought he knocked it on but it looks to have gone backwards," Powell said. "Whether it hit the line or not is hard to tell.
"We've just got to look at ourselves. Somebody had to catch that ball and we should have scrambled a bit harder."
Powell says he was forced to change his team the day before the game after prop Suaia Matagi pulled out through illness, with Alex Foster taking his place on the bench.
"It's disappointing for Suaia," Powell said. "I thought he would have had an impact today."