The game had finished goalless after 90 minutes, with Dikwena understandably having the better of the game against their lower league opponents, who also had Tshepo Moletsane send off on the hour-mark.
The game really sprung to life in extra-time, with Eleazar Rodgers giving Stars the lead on 96 minutes when he converted a cross from the right.
The lanky striker almost made it two from a similar situation minutes later, before Steenberg got their equaliser with 10 minutes remaining - Robin Rhode finishing after a goalmouth scramble.
The game went to penalties, where former Ajax Cape Town and Orlando Pirates striker Fanteni missed the only effort to send Dikwena through to the next round.
Steenberg United: Kock, Mobara, Pieterson, Mkhize, Stanfield (Matiwane 68), Maqoko, Bernard, Lumkwana (Fanteni 46), Bantam (Mxabo 79), Rhode, Moletsane
Platinum Stars: Mzimela, Semenya, Sithole, Nhlapo, Zulu (Tshabalala 62), Madondo (Gumede 75), De Jongh, Segolela (Kodisang 75), Ng'ambi, Zongo, Rodgers