Ian Bell led England to a comfortable victory to keep them at the top of the ICC ODI rankings, after a fine bowling performance had restricted the target to just 221.
Bell batted with panache to make 88 and Eoin Morgan's 36 not out took England over the line after South Africa had set a less than convincing target in an innings which faltered following a strong beginning.
The tourists, searching for a win which would have once again taken them ahead of England to top the rankings, had reached 100/1 after a combination of dropped catches and fortune had helped them through tricky early overs.
But fine bowling from Ravi Bopara and James Tredwell saw four wickets fall for 15 runs, and despite some resistance from Ab de Villiers, Dean Elgar and a 20-ball 31 not out from Robin Peterson, SA's total was well below par.
Craig Kieswetter's six into the Pavilion off Dale Steyn secured the victory and made sure England will remain the top-ranked team regardless of the result of the final ODI at Trent Bridge.
Ebb and flow
England's poor catching this summer continued earlier in the day, as Tredwell dropped both South Africa openers early on in the slips after Alastair Cook had won the toss and elected to bowl under grey skies.
Tredwell made up for both dismissals though with a fine bowling performance on a turning track, which produced three stumpings for Kieswetter - including that of the captain AB de Villiers. Ravi Bopara was once again excellent with the ball, picking up 2/34 in nine overs as England strangled the tourists in the middle overs.
They relied on a 20-ball 31 not out from Robin Peterson to get them to a reasonable score though - the cameo including a magnificent switch-hit off Tredwell for a big six.
Cook, England new Test skipper, has been out of form in the second half of this summer and was trapped LBW in Steyn's first over of the reply, but Jonathan Trott overcame a painful blow to the hand (for which he will receive an x-ray tomorrow) in a 141-run partnership with Bell.
It was far from fluent from the pair, but Bell decided that taking some risks would be the right strategy to keep the scoreboard moving. He flashed hard and was happy to advance down the track to the quick bowlers.
Trott was clearly uncomfortable throughout his innings, but he ticked along before falling to Dean Elgar for 48. Umpire Simon Taufel originally said not out to an LBW appeal, but the Proteas used their review wisely (unlike Steven Finn and England earlier in the day) and HawkEye revealed Trott to be plumb.
Bell played some fine strokes, hitting eight fours and one notable six as he stroked Peterson inside out over extra cover for the maximum. But a brief rain shower appeared to ruin his rhythm, and was well caught by de Villiers off Steyn, top edging as he advanced down the pitch.
It left a potentially nervy finish for England, but Morgan is the master of ODI run chases. He chose to attack McLaren after Steyn was taken off and the Dubliner hit him for three fours before Kieswetter continued the assault, finishing things off with a stunning straight six which disturbed the MCC Members sat in front of the Pavilion.