It was a ghastly couple of seconds and, as the ball flew towards Peterson, carried a terrible certainty of the outcome.
This may sound tough on Brownlie, who had batted with courage, a pleasing counter-attacking mindset and got his test career back on track after losing his way in the West Indies last year.
Nevertheless, New Zealand had got back into a position where, trailing by 73, they were five wickets in hand and with two batsmen well set.
It is hard to underestimate how much it would have meant to have made South Africa bat again. It may be brutal considering all he'd put in to that point but that ended with Brownlie's departure. From the ashes of 45 all out, it would have been some form of confirmation that New Zealand were capable of far better.
Instead, with Brownlie's blunder, it signalled the end for New Zealand. The last five wickets fell for 23.
The thought persisted: would a South African batsman have committed such a howler, at such a point in the contest?
It wasn't so much that it happened - all players make mistakes, otherwise there'd be no game - but when. Midway through a session is one thing; five minutes from sandwiches and tea, given the backdrop of what had gone before and what progress had been made in the preceding couple of hours, quite another.
Brownlie suffered for letting his mental guard down for a split second.
By chance, a couple of hours later, South Africa's captain Graeme Smith was being asked about his team's steely mentality. Set aside ODI cricket. South Africa have never won a knockout game at the World Cup. Something's wrong there.
But the test game is different. When in difficulty, the world No1 side have long had the wherewithal to find a way out. Go back to Sydney in 1994, when defending just 117, South Africa never let up and when Fanie de Villiers clutched a return catch from last man Glenn McGrath, they'd won a famous victory by five runs.
At Adelaide late last year, Faf du Plessis oversaw a remarkable salvage job with an eight-hour century on debut to save the match. South Africa's crushing win at Perth a few days later ensured they'd hold onto the No1 spot.
That's just two of many examples of South African teams being able to utilise that mental hardness that New Zealand teams, by and large, seem to have no chance of attaining.
Is it some quality in the DNA of the nation's cricketers or something they weld on when players join the national team?
"It's a tough one," Smith said. "Everyone will have a different theory on mental toughness, but it's ingrained in us now. We've been in a lot of tough situations and the guys have performed around the world. You get a bit of that from training in tough situations, and an honesty.
"The biggest thing for me is an understanding of knowing what to do in every situation and be man enough to go and do it. I think we're a mature team, we've grown up now. We've come through a lot together and are ready hopefully to take the next step."
New Zealand, he said, have some good players but they're a young team and have much to do. They are No8 playing No 1.
"They are obviously a growing team and it's my job and rest of team to keep them under pressure for the rest of the summer," Smith said.