Spurred on by De Kock, South Africa needed just 27.2 overs to reach 171-3 and easily chase down Zimbabwe’s 165 all out at Queens Sports Club.
De Kock plundered seven fours and two sixes and appeared to be racing to a sixth century of his young career when he smashed a catch straight to Sean Williams near the mid-wicket boundary with South Africa only 22 short of the target.
JP Duminy finished the game with a six to end 28 not out as the Proteas cruised to a fourth success in Zimbabwe after also winning the one-off test. Stand-in captain Faf du Plessis made 40.
“I’m enjoying every moment of it,” De Kock said of his rich vein of form. He was named man of the series.
South Africa rested a string of top players through the series in Bulawayo and was still a class above the Zimbabweans.
Front-line fast bowlers Dale Steyn, Vernon Philander and Morne Morkel sat out the entire ODI series ahead of a triangular tournament also involving Australia. Regular ODI skipper AB de Villiers and Hashim Amla were rested for the final game. Without them, South Africa still retained its record of winning every ODI series it has contested against Zimbabwe.
The second-string pace attack of Marchant de Lange, Kyle Abbott and Wayne Parnell was easily good enough on Thursday.
Abbott removed Zimbabwe opener Hamilton Masakadza in the first over, De Lange (3-31) took a wicket off the first ball of the second over, and the Zimbabweans never recovered from being 4-2.
At 119-9 the home team was destined for a much lower total until some late hitting by captain Elton Chigumbura in a last-wicket partnership of 46 with Tinashe Panyangara. Chigumbura made 90 with 10 fours and two sixes and launched some big shots before he had his off stump knocked back by De Lange trying another heave to the leg side.
Facing the modest total, De Kock looked likely to take South Africa charging to victory. He advanced down the track to stroke fast bowler Panyangara over mid-off for six in his best shot. But he hit the next delivery low and hard to Williams to get out.
It made no difference, with Duminy and David Miller (13 not out) seeing South Africa to a comfortable win.
“Very happy,” stand-in skipper Faf du Plessis said. “We started this series wanting to beat Zimbabwe convincingly. To do it 3-0 and in the fashion we finished the game off today, I’m very happy.”
South Africa, Zimbabwe and Australia will now contest a triangular series in Harare starting next week.
“I think our batting has to improve,” Zimbabwe captain Chigumbura said.