An unbeaten century from skipper AB de Villiers helped South Africa to a six-wicket win over New Zealand in the first one-day international in Wellington.
The tourists looked to be in trouble at 35-3 when De Villiers (106 not out) came in, but he put on 90 with JP Duminy (46) to steady the ship, then shared an unbroken 129 with Faf du Plessis (66no) as the tourists made short work of New Zealand's 253-9.
That total came on the back of half-centuries from Brendon McCullum, who rode his luck in the early stages of his innings to reach 56, and rising star Williamson, who made 55.
Lonwabo Tsotsobe had Martin Guptill caught behind - and thought he had trapped new man McCullum leg before, shouldering arms to the next ball, only for the batsman to overturn the dismissal on review.
DRS saved McCullum again after he was initially adjudged to have edged Robin Peterson to keeper De Villiers, and the Kiwi skipper brought up his side's 50 in the 14th over.
Peterson soon struck as Rob Nicol edged to Jacques Kallis at slip having made 30, before McCullum broke out of his shell with his first boundary as he hit his 42nd delivery over mid-wicket for six.
Another maximum followed before two fours in successive overs saw him to his half-century from 62 balls, but his innings came to an end soon afterwards when he hoisted Kallis to the cover-point boundary, where Peterson took a well-judged catch diving forwards.
Jesse Ryder fell cheaply, but Williamson made an impressive 59-ball half-century, before edging to De Villiers soon after.
South Africa were quickly in trouble in their reply as Hashim Amla was bowled by Tim Southee, Graeme Smith edged Kyle Mills to slip and Kallis pulled Bracewell to square leg.
South Africa had to rebuild and Duminy claimed two fours in three balls off Andrew Ellis, but was soon afterwards caught and bowled by Nicol four runs short of 50.
South Africa were 125-4 at that point with 20 overs to go and the game in the balance.
But De Villiers resolutely passed 50 and heaved a huge six off Nicol two overs later - before Du Plessis survived being given out lbw when the DRS showed the ball was going over the stumps.
That proved a turning point as a flurry of boundaries saw South Africa speed towards their target, typified by successive sixes which De Villiers plundered off Nicol.
De Villiers reached his faultless 100 in 101 balls, and De Plessis hammered Bracewell for six to pass 50 in an over which cost 16.
New Zealand were beaten by then and a Du Plessis single gave South Africa a victory which puts them 1-0 up in the three-game series.