The young Welshman came on to replace the injured Rob Kearney at full back in the 65th minute and within a minute was given the chance to kick for goal from the half-way line.
That kick, to the right of the posts and into the swirling wind, didn't go well. It was a different story, though, with three minutes left to play and the scores tied at 23-23.
Acting skipper Martyn Williams asked Hook and Stephen Jones if they fancied having a go for goal from 50 metres and the Osprey said 'no problem'.
"We could have gone to the corner and I knew it was a long way out. But James took the decision out of my hands by saying 'no problem'," said Williams..
"It was a real pressure kick and he hit it beautifully. A great kick in the conditions."
The rain had stopped at that stage, but the wind was still swirling around the Newlands ground and the crowd were screaming their heads off. But Hook blanked it all out and did what had to be done.
"I just concentrated on getting the strike right. I knew it was at the end of my range, but I also knew that if I struck it well it would go over," said Hook.
"It was one of the most important strikes of my career. I just got into my routine and thought about what I do every day back home when I'm training at The Gnoll in Neath.
"I struck it well and it went over to win the game for us. If we had drawn, it would have felt as bad as a loss, but the victory keeps out momentum going and it was a massive boost for us."