It was New Zealand's second win in eight T20s against England and McCullum's first T20 half century in 10 innings was just the tonic for his bowlers to produce a committed display to reduce England to 47 for five.
"I'm just happy to have made a contribution," McCullum said.
"There were other contributions which shouldn't go unnoticed. I just try and play a role as a batsman first and foremost, and as captain it's nice to make a contribution as well."
McCullum had high praise for openers Martin Guptill and Hamish Rutherford, with their 75-run partnership, which got the innings moving.
McCullum oversaw a late flurry, with 38 off the final two overs getting New Zealand to a position the bowlers could work with.
Ian Butler, at 31 and in his first match for New Zealand in two years, was outstanding, taking two for nine off his four overs, with left armer Mitchell McClenaghan knocking the top off the England innings and James Franklin's cheap four wickets wrapping up the job.
"I thought Butler was brilliant. The way he got his wickets as well," McCullum said. "He hurried the batsmen, managed to bowl at a reasonable pace and get bounce. I'm really delighted for him."
McCullum said New Zealand knew where they had to step up after England's equally convincing 40-run win in the opening game at Eden Park last Saturday.
"We were all disappointed with the other night's performance. Even though we've got young fellows in the team, we're savvy enough to know T20 can be turned around pretty quickly. We knew were we needed to improve."
However McCullum is expecting England - much as New Zealand did at Seddon Park - to hit back hard in Wellington.
"You only have to be a little bit off and there's a bit of a gulf between the sides. We know England are going to come back strong, so we have to ensure we go up again."
England captain Stuart Broad praised New Zealand's display, but expects his team to smarten up for Wellington.
"I thought they batted really well. It takes a lot of skill to hit the ball like the New Zealand players' did," he said.
"When you have a loss obviously you look at what we did wrong and try to improve.
"We weren't quite as clinical with our plans and skills and New Zealand were.
"Obviously they've had a really good day. We need to look back and make sure we get our standards right for Friday."
