South Africa and West Indies must return to The Oval on Sunday to complete their Champions Trophy Group B decider after rain continued to blight the tournament.
South African opener Herschelle Gibbs returned to form to hit a composed century and lead South Africa to 246 for six before rain stopped play for the day with West Indies 20 without loss in reply after six overs.
Gibbs had a torrid time with the bat in last month's tour of Sri Lanka and was in danger of the axe but he hit back with 101 from 135 balls, including a six off spinner Chris Gayle to bring up his hundred.
He fell in the same over, however, caught on the long off boundary by Dwayne Bravo and the dismissal heralded a flurry of wickets with the South Africans hitting out to boost the score towards the end.
Captain Graeme Smith earlier struck 45 in a 102-run opening stand with Gibbs before he was bowled by Gayle, who later grabbed his third wicket when Jacques Rudolph (46) missed a sweep.
The West Indies attack was blunted by the loss of injured pace bowler Mervyn Dillon, who took a career-best five for 29 in the victory over Bangladesh last Wednesday.
The winners face Pakistan or India in Wednesday's second semi-final in Southampton.
Earlier, England beat Sri Lanka on the Duckworth/Lewis method after their game Group D was washed out on the second day in Southampton. England will meet Australia in the other semi-final on Tuesday.
