Nick Compton scored an unbeaten 102, sharing an opening stand of 231 with Alastair Cook, as England fought back to within 59 runs of New Zealand in Dunedin.
"After getting nought in the first innings I had to pull something out of the bag," the Somerset player said.
"I never thought I would be standing here with a hundred to my name. It's the biggest relief of my life."
He was dismissed for a duck in the first innings in Dunedin and came out to bat in the second with England 293 behind after New Zealand scored 460-9 declared in reply to England's 167.
"The 90s were horrible," he admitted. "It was probably one of the worst hours, and it felt like two hours.
"But the bigger picture was the game and I wanted to make sure I kept my eye on the ball.
"It would have been easy to try to run down and have a flap at the spinner before the new ball but I thought it was important that I stayed here.
"I never thought a year ago or [even] a couple of months ago I'd be sitting here right now with a hundred.
"I kept believing, but it's been a long time. It's a strange feeling but I'm just delighted to be here.
"You just know instinctively what you need to do, and I felt like this innings was very important."
But Compton knows there is still work to do on the final day.
"We've got another day to go and they are going to come hard at us, but we've just got to try to do a bit of what we did today," he said.