The hosts went into the break with a narrow 16-8 advantage but Jack delivered the killer blow in the 44th minute when the peerless All Black lock scored following an attritional drive from the Crusaders.
McCaw said: "It was a bit of an arm wrestle in the first half. There was a lot of kicking, so as a forward I got caught in the middle a fair bit.
"We knew we had to meet the physical side of things and to a large extent we did and scored a few tries in the second half.
"We felt we'd played a bit but there was still a fair bit left in the tank to come out and put them under pressure.
"As for the try just after half-time, we wanted to keep it pretty tight in the forwards and that started the second half off pretty well."
Visiting skipper Victor Matfield agreed, telling Sky Sports: "We were still in it at half-time. We made two turnovers in the first half and they punished us.
"But their try after the break, following 17 phases, was awesome play and that try put us out of the game.
"You need to get over the advantage line but we couldn't do it. Their defence was very good."