Gibbs, with just 16 runs in the previous three matches, scored a solid 77 to bolster the innings after South Africa had found runs hard to come by against a tidy West Indies attack.
The middle-order batsman added 92 off 108 balls for the fourth wicket with AB de Villiers (46) after his team had lost skipper Graeme Smith, Loots Bosman and Jacques Kallis for 96 runs Thursday.
South Africa were then steadied by Gibbs, playing his first tournament in India after being named in the 2000 match-fixing scandal. He had already skipped two tours to the country.
Gibbs adjusted himself remarkably well on a slow pitch, picking the right deliveries to punish during his 26th half-century in 190 one-dayers. He struck one six and four boundaries before falling in the last over on 77.
Fast bowlers Jerome Taylor and Dwayne Bravo, and off-spinner Marlon Samuels grabbed two wickets apiece.
The winners will meet world champions Australia in the final at Mumbai on Sunday.
South Africa, whose highest total in the last three games was just 219, began impressively when they added 27 in the opening five overs through Smith and Bosman.
Taylor provided the breakthrough when he removed Smith, who was bowled off his pads after contributing 19. The South African captain has so far made 71 in four matches of the ongoing tournament.
Like his captain, Kallis (16) also had yet to score big. He was caught slashing Bravo at third-man by Ramnaresh Sarwan. He has made only 84 in four matches.
Opener Bosman gave a good account of himself in his first match of the tournament, scoring a neat 39 before being caught off a leading edge by Chris Gayle in the covers.
But Gibbs kept his end intact with a sensible knock, helping his team score 76 in the closing 10 overs.