The tall 21-year-old, who grew up a wicketkeeper and took up bowling six years ago, admitted some of the wickets taken yesterday wouldn't rate up among the great balls of test history.
"It was a little bit inconsistent, but I'm happy with how it went in the end."
McCullum paid tribute to the unbroken stand of 80 between Dan Vettori and Dean Brownlie.
"Without that partnership we'd be in deep trouble. They managed to put us back in the game a little bit," he said.
McCullum was disgusted at getting out to a loose shot, having done the hard work through the first hour and getting to 34. There had been no collective batting strategy, more a case of players being true to their nature.
"We're all pretty upset to pass up an opportunity to score big runs on a challenging pitch against a very good team.
"I can't stress enough it's not so much the deliveries that got us out; more the buildup of pressure. That's where we came unstuck."
McCullum described New Zealand as being "slightly behind the 8-ball, but we're going okay. Tomorrow is a big day for us to step up and put ourselves in a strong position tomorrow night".