Fly-half Steyn kicked a conversion and three penalties and winger Jacobs scored two tries in searing heat at Loftus Versfeld stadium with the total completed by a try from hooker Johan Grobbelaar.
In Cape Town, Sharks fly-half Curwin Bosch contributed 14 points from a conversion, three monster penalties and a drop goal in a 19-9 triumph over hosts Western Province in the other semi-final.
It was a disappointing goodbye for Province to Newlands, a 133-year-old stadium hosting its final professional rugby match before being demolished.
Province are moving to Cape Town Stadium, a venue built for the 2010 FIFA World Cup that offers state-of-the-art facilities, unlike decaying Newlands.
The Currie Cup final will be the first between the Sharks and Bulls since the Durban team won 14-9 at home 13 years ago.
In Pretoria, ill discipline cost the Lions dearly as they fell to the Bulls for the third time since the domestic season kicked off last October after a long coronavirus-induced delay.
They conceded far too many penalties and locks Marvin Orie and Willem Alberts were yellow-carded within two minutes of each other during the second half, reducing the Johannesburg outfit to 13 players.
While the visitors were two men short, Jacobs scored his second try, which ultimately proved the difference between the teams.
In a match riddled with stoppages, the Bulls built a 14-0 lead soon after half-time only for tries from Alberts and centre Wandisile Simelane to draw the Lions level on 48 minutes.
Bulls were back in front nine minutes later thanks to a Grobbelaar pushover try and the hosts went 26-14 ahead when Jacobs scored.
A Lions rally when back to full strength was finally rewarded three minutes after the hooter sounded for full-time with former Bulls centre Burger Odendaal scoring his first try of the Currie Cup campaign.
Meanwhile, a mixed outing for Bosch began embarrassingly when his kick to start the match did not go the minimum 10 metres and the Sharks were penalised.
His evening took a turn for the better, though, as he slotted three penalties, one from halfway and the others from inside his half.
Bosch later suffered another awkward moment when he took several steps beyond the mark before taking a free-kick and was penalised.
Province dominated first-half possession and territory only to trail 9-6 at half-time, but they equalised early in the second half when fly-half Tim Swiel kicked his third penalty.
Bosch put the Sharks ahead again with a drop goal — the first in the Currie Cup this season — and lock JJ van der Mescht barged over for a 73rd-minute try to seal success.
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© Agence France-Presse
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