Quinton de Kock hit a blistering half-century and Kagiso Rabada scalped three wickets as South Africa defeated a battling United States by 18 runs in their opening T20 World Cup second round clash on Wednesday.

The Proteas piled up 194-4 off their 20 overs after being put into bat before restricting the USA to 176-6 as the Super Eights stage got underway at the Sir Vivian Richards Stadium.

However, the USA, who stunned former champions Pakistan in the first round, were close to another upset when Andries Gous (80 not out) and Harmeet Singh (38) put on 91 for the sixth wicket.

Opening batsman De Kock, his country's leading run-maker in the format, reached his 15th T20 international fifty off 26 balls.

He was eventually dismissed for 74 with seven fours and five sixes in a 40-ball innings which was comfortably his best performance of the tournament.

In four previous visits to the crease at the World Cup, the 31-year-old had a best of just 20 against Sri Lanka.

Skipper Aiden Markram also hit his tournament best of 46 from 32 balls with four boundaries and a six.

Markram and De Kock put on 110 for the second wicket and helped their team reach 101-1 off the first 10 overs.

Slow left-armer Harmeet brought the United States back into the match by removing De Kock and fellow dangerman David Miller (0) in the space of two balls.

Markram's innings was ended by impressive fast bowler Saurabh Netravalkar who finished with 2-21 from his four overs.

Gous, Harmeet give hope

Heinrich Klaasen (36 not out) and Tristan Stubbs (20 not out) added an undefeated 53 for the fifth wicket.

The United States enjoyed a bright start to their reply on Wednesday, reaching 50 in the first five overs before they struggled to contain the Proteas' pace-spin attack.

Rabada removed Steven Taylor (24) and Nitish Kumar (eight) before American hopes suffered a major blow when skipper Aaron Jones was out without scoring.

Jones had smashed an undefeated 94 in the first round win over Canada but lasted just five balls Wednesday when he edged spinner Keshav Maharaj to De Kock.

Former New Zealand international Corey Anderson made a quick 12 before his stumps were scattered by Anrich Nortje one ball after cracking a six over midwicket.

The USA limped to 73-4 off the first 10 overs before opener Gous and Harmeet suddenly reignited their team's hopes.

Gous smashed leg-spinner Tabraiz Shamsi for three sixes in the 18th over to leave his team needing 28 off 12 balls.

Rabada, however, conceded just two runs off the 19th over while also dismissing Harmeet to finish with 3-18.

Harmeet made his runs from 22 balls with two fours and three sixes.

Gous's runs came off 47 balls and featured five fours and five sixes.

Shamsi went for 50 runs off his four overs.

West Indies and defending champions England are the other teams in Group 2 of the Super Eights.

India, Australia, Afghanistan and Bangladesh comprise Group 1.