Mark Boucher made an equally vital 34 as South Africa recovered after a miserable start - which saw them 68 for 6 - to make 221 for 8 on a Newlands pitch offering bounce and movement.
Hansie Cronje, the South African captain, won the toss and elected to bat on a pitch that ended up playing very slowly, making stroke play difficult. Nixon McLean did the early damage, taking all three wickets as the home side were reduced to 50 for three by the 15th over.
Keith Semple, a medium-pace bowler, continued to apply the pressure and took two quick wickets including that of Cronje, caught behind for two in his 100th one day international as South African captain. Curtly Ambrose claimed the wicket of Jacques Kallis with a slower ball to leave South Africa's much vaunted lower order facing a major rebuilding operation.
Benkenstein - run out on the last ball for 69 - added 62 in 17 overs with Boucher who edged an Ambrose delivery to the wicketkeeper. Klusener, an all-rounder, then came to the wicket at 130 for 7 with ten overs remaining. He hit three sixes and two fours in a bruising South African eighth wicket record partnership of 91.
The last two wickets added 153 in 27 overs. South Africa lead the best of seven series by three matches to one.
South Africa won toss
G Kirsten c Jacobs b McLean 4
H H Gibbs b McLean 17
J Kallis lbw b Ambrose 16
S Pollock c Chanderpaul b McLean 8
H Cronje c Jacobs b Semple 2
J Rhodes c Arthurton b Semple 9
D Benkenstein run out 69
M Boucher c Jacobs b Ambrose 34
L Klusener not out 54
Extras (lb4 nb-1 w3) 8
Total (for 8, 50 overs) 221
Fall: 1-10 2-35 3-50 4-52 5-52 6-68 7-130 8-221.
Bowling: McLean 10-0-41-3 (3w); King 9-1-39-0; Ambrose 10-0-38-2; Semple 10-0-35-2 (1nb); Arthurton 6-0-31-0; Hooper 5-0-33-0.
n David Terbrugge, the South African seamer, has withdrawn from the forthcoming tour of New Zealand because of an ankle injury. The 22-year-old will be replaced by the veteran all-rounder Steve Elworthy, 32.Reuse content