Ravindra made 108 off 101 balls and Williamson hit 102 off 94 deliveries, as New Zealand posted a Champions Trophy record 362-6 before restricting South Africa to 312-9.
David Miller finished unbeaten on 100 but his 67-ball blitz came in vain with the game already well out of reach, as South Africa suffered their fifth Champions Trophy semi-final defeat after those in 2000, 2002, 2006 and 2013.
They won the first edition of the tournament in Bangladesh in 1998, when it was named the ICC KnockOut Trophy.
New Zealand captain Mitchell Santner excelled with the ball and took 3-43 with his left-arm spin, breaking a 105-run partnership for South Africa’s second wicket by removing rival skipper Temba Bavuma for 56.
Bavuma started slowly but steadied the innings with Rassie van der Dussen, who scored a fluent 69 before being deceived by a beautiful delivery from Santner.
Santner then dealt a critical blow when he dismissed Heinrich Klaasen for three, caught by a diving Matt Henry at long-on, dashing South Africa’s hopes of pulling off the highest chase in the tournament’s history.
Ravindra had Aiden Markram caught and bowled for 31 while Glenn Phillips chipped in with 2-27 as South Africa crumbled against spin.
“It’s a cool feeling to make the final,” said Santner. “We were challenged by a good side and now we’ve had a go against India, look forward to do it again.”
New Zealand last won an ICC ODI men’s event in 2000, beating India in the final of that year’s Champions Trophy in Kenya. India won by 44 runs when the teams met in the group phase last Sunday in Dubai.
Bavuma said New Zealand were simply too good for South Africa on Wednesday.
“New Zealand were above par,” said Bavuma. “We backed ourselves to chase 350 with the wicket getting better but they really put us under pressure from the get-go.”
Ravindra and Williamson set the foundations for a big total on a batting-friendly Gaddafi Stadium pitch after New Zealand won the toss and batted first.
Daryl Mitchell clubbed 49 off 37 balls and Phillips smashed a 27-ball 49 not out as the Black Caps plundered 110 runs in the last 10 overs and 66 in the last five.
South Africa’s bowling line-up struggled right from the start as Ravindra and Will Young (21) put on 48 for the opening stand.
It was followed by a magnificent 164-run partnership for the second wicket between Ravindra and Williamson that put the New Zealanders on track for a massive total, as the duo scored at will with some delightful strokes.
Ravindra completed his fifth ODI hundred – all coming in ICC events – from 93 balls with a two off Kagiso Rabada.
Williamson reached his 15th ODI hundred with a ramped boundary, his third three-figure score in as many matches against South Africa.
It was Rabada who finally ended the partnership by dismissing Ravindra caught behind. Ravindra hit 13 fours and one six in total.
Williamson chipped Wiaan Mulder into the hands of Lungi Ngidi in the 40th over after hitting 10 fours and two sixes.
Mitchell and Phillips added some late impetus after South Africa had briefly dragged things back to give themselves hope of limiting the score to under 350.
Fast bowler Ngidi finished with 3-72, while Rabada ended with figures of 2-70. (AFP)
