But Sciver-Brunt, back after missing the last three group games with a calf injury, counter-attacked to the delight of a crowd of over 21,000.
She received excellent support from former skipper Heather Knight (58) as the two survivors from the last England side to win a major international trophy — the 2017 50-over World Cup — turned the tide with a fourth-wicket partnership of 133 that took their team to a total of 169-5.
Tournament hosts England will play arch-rivals Australia in Sunday’s final at Lord’s. Both sides have won all six of their matches.
A chase of 170 was always going to be a tough task for South Africa and they finished well short on 129-8.
“I was probably nervous, the occasion gets quite big as well and so that increased the nerves,” said Sciver-Brunt, the player of the match, at the presentation ceremony. “I missed a few games (with my injury). There was a lot of emotion pre-game.”
‘Got our heads together’
She added: “Marizanne Kapp and Shabnim Ismail are world-class opening bowlers who can do some damage. So Heather and I wanted to nullify the threat and make sure we were in and able to capitalise on other bowlers. We used our experience, got out heads together and got the job done.
“We showed composure. We could have tried to go harder earlier and it might not have worked out, so we were really smart.”
Kapp took 1-16 in her maximum four overs and Ismail 2-31.
But Ayabonga Khaka’s and Nadine de Klerk’s combined seven wicketless overs cost 79 runs.
South Africa captain Laura Wolvaardt said her side had been “outplayed”, adding: “We were happy with 170, which we thought was par. They bowled well, had good plans and we weren’t able to step up.”
Earlier, South Africa enjoyed a brilliant start by taking three England wickets inside the first four overs.
Fast bowler Ismail struck with her first ball, Amy Jones cutting straight to point.
England opener Danni Wyatt-Hodge, whose previous five innings had yielded a tournament record 282 runs at a stellar average of 94, was bowled for just 12 by Kapp’s well-disguised slower ball.