"Dean was brilliant. It was a high quality innings that in the circumstances was fantastic for him and hopefully is the start of a very successful career for him," he said.
McCullum said it was important New Zealand grasped the positive aspects of the test - "the way we responded on the second day, firstly with the ball then getting through to 160-odd for four was a remarkable improvement form the previous day.
"We've seen that we can put some pressure on them if we can do those hard yards up front."
The day began with New Zealand 169 for four, 133 adrift of making South Africa bat again.
Brownlie and BJ Watling put on a gutsy 74 for the fifth wicket before Brownlie played a rash shot five minutes before lunch and was caught at deep point.
Watling's dismissal for 42 after 211 minutes at the crease, signalled the end was at hand. The last five wickets fell for only 23 runs.
South Africa's fast bowlers piled on the short-pitched bowling and James Franklin and Jeetan Patel both received fierce blows on the body from Dale Steyn.
When Steyn dismissed Franklin he had his 50th wicket against New Zealand in his ninth test.
Of the bowlers, Steyn took three for 67 and there were two apiece for man of the match Vernon Philander and Jacques Kallis.
New Zealand will now regroup ahead of the second and final test, starting in Port Elizabeth on Friday. Putting aside the memory of that first day at Newlands will be a challenge.
"It hurts immensely. We've got a very disappointed bunch of lads," McCullum said.
It is New Zealand's 22nd test loss in 39 matches against South Africa.
