Hull, who led 18-0 after 14 minutes, produced a magnificent rearguard action to hold on for a 26-24 victory following prop Liam Watts’ dismissal in the first half.
“I am really, really pleased,” Radford said.
“Prior to the game I asked them to put a performance together we are worthy of.
“Up until the Liam Watts sending off I thought we were well on top with 13 men on the field.
“When we went down to 12, the willingness to scramble for each other was outstanding – it was an unbelievable effort.
“They got a huge lift from Liam going off. We weren’t as tight as we needed to be for a period after that and they scored some points, but in the second half that willingness to turn up for one another was a blueprint of what we needed.
“I also asked during the week for the supporters to show some vocality and I can’t tell you how many times they picked us up when we needed it. I was really proud of that as well.”
Watts was dismissed for a high tackle on Castleford’s England half-back Luke Gale, who did not return to the action.
Radford refused to be drawn on his opinion of the incident. He said: “I just think the official has done his absolute utmost to put controversy on that game of rugby league when it wasn’t needed.”
Castleford coach Daryl Powell felt his team were “dumb”, but he praised Hull’s performance.
He said: “It is really disappointing. I thought it was our worst performance of the season by a distance. I wouldn’t take anything away from Hull. To play with 12 men as long as they did was an awesome effort. As dumb as we were, they were desperate. It was a fantastic effort from them.”