South Africa beat the United States by 18 runs in the first T20 World Cup Super 8 game in Antigua on Wednesday as Kagiso Rabada's experience came to the fore at the end of a tense game.

Having struggled on New York's slow pitches in the group stage, South Africa scored freely at the Sir Vivian Richards Stadium, posting 194-4 on the back of Quinton de Kock's fine knock of 74.

In response, U.S. opener Andries Gous (80 not out) provided the fireworks along with Harmeet Singh (38) down the order but fast bowler Rabada picked up crucial wickets in his spell of 3-18 and restricted the run rate as the U.S. fell short.

"We've had some tricky wickets coming up to this game and I think it's just nice to spend some time out in the middle," said De Kock, the player of the match.

The U.S. had won the toss and opted to field first, picking up the wicket of Reeza Hendricks early but De Kock cut loose as South Africa scored at over 10 runs per over during the powerplay.

De Kock reached his fifty in 26 balls and shared a 110-run partnership with skipper Aiden Markram off 60deliveries.

Harmeet Singh dismissed De Kock when he mistimed a full toss and was caught near the boundary and the all-rounder was on a hat-trick when he had David Miller caught and bowled.

Superb spell

Markram fell four runs short of his fifty when he chased a wide loose ball and Ali Khan took a sharp diving catch to give Saurabh Netravalkar his second wicket.

Despite Netravalkar's superb spell (2-21), the others failed to contain South Africa as Heinrich Klaasen dealt in sixes and scored a quick-fire 36 in an unbroken 53-run partnership with Tristan Stubbs (20) to propel them to 194-4.

American opener Steven Taylor (24) underlined his intent when he smashed a boundary off the first ball, but after four fours and a six, he fell to Rabada when a mistimed shot was caught at mid-off.

The fast bowler also dismissed Nitish Kumar, who was caught at deep square leg, and U.S. captain Aaron Jones fell for a duck to spinner Keshav Maharaj.

Gous continued to resist, bringing up his fifty with back-to-back sixes, but the required run rate continued toclimb.

There was hope when Shamsi went for 22 runs in an expensive 18th over but Rabada returned to dismiss Harmeet, conceding only two runs in the penultimate over.

"It's hard to take the defeat after getting so close. We could have been a little more disciplined bowling-wise," Jones said.

"It could have been a closer game and we could have got over the line."