Brownlie defied the Proteas attack to reach stumps unbeaten on 69 and duly continued his resistance on the third morning to reach three figures for the first time.
But on the verge of lunch, and with South Africa's mammoth 302-run first-innings lead starting to come into sight, he recklessly uppercut Morne Morkel to deep point to depart for 109. New Zealand were therefore left still very much second best, at 232 for five.
With BJ Watling content to stonewall, his unbeaten 31 occupying 114 balls, Brownlie took a more assertive role as he eyed a first century in his eighth Test.
The Australia-born batsman showed no signs of nerves as he approached the milestone, moving to 98 with a pulled six off Robin Peterson before dancing down the wicket and clearing the rope over mid-off from the same bowler to prompt his celebrations.
For the first time New Zealand had started to take a lead role in the match only for the second new ball - taken with just two overs to go before lunch - to end Brownlie's memorable century.
The 28-year-old's departure undermined the work he had done beforehand as he slashed at Morkel, picking out Peterson on the rope, to ensure South Africa remained well on course for victory inside three days.