The Proteas bowlers came to the party after captain Temba Bavuma had won toss and chose to field, dismissing the Dutch for just 189 in 46.1 overs.
Bavuma then led from the front with the bat hand as he smashed 90 not out off just 79 deliveries while Aiden Markram struck an unbeaten 51 from 39 balls as the Proteas romped to the win with 20 overs to spare.
The visitors got off to a decent start with the willow as openers Vikramjit Singh and Max O'Dowd (18) put on 58 within the first 11 overs.
Sisanda Magala came into the attack and broke the stand when the seamer had O'Dowd flashing outside off-stump and found the edge to be caught wicketkeeper Quinton de Kock.
Singh was looking in fine touch as he made his way to 45 off 53 deliveries that included three towering sixes but Magala once again did the job for skipper.
The visitors then seemed to get stuck after the initial two wickets fell as the hosts smelt blood and continued to plug away, striking telling blows a regular intervals.
Spinner Tabraiz Shamsi came into the attack in the middle overs bowled 10 overs for just 25 runs while also claiming three wickets.
Teja Nidamanuru, batting at number six, put up some resistance for 48 off 71 balls but Magala had him caught behind.
That wicket denied the Netherlands the impetus to make a late charge as Magala finished with figures of 3-37 in eight overs while fast bowler Anrich Nortje took 2-24.
The Proteas lost De Kock (9) early in the run-chase, the left-hander top-edging a sweep off spinner Aryan Dutt in the sixth over.
Rassie van der Dussen (31) added 70 with Bavuma for the second wicket but the number three was beaten for pace by seamer Fred Klaassen to loop a simple catch on a pull shot.
Bavuma and Markram though calmed any nerves the hosts might have had with the duo going on the counter-attack that paid off handsomely with unbroken partnership of 102 off 69 balls.
The victory sees the Proteas jump to ninth in the ICC Super League table and another win over the Dutch in the final ODI at the Wanderers on Sunday should see them move into the top eight that ensures an automatic place in the World Cup that takes in India later this year.