(Saint Lucia) - Anrich Nortje held his nerve as South Africa remained unbeaten at the T20 World Cup after defeating reigning champions England by seven runs in a thrilling second-round Super Eights clash in St. Lucia on Friday.

England, chasing a seemingly modest 164 to win, slumped to 61-4 thanks to fine South Africa bowling and fielding before a partnership of 78 between Harry Brook (53) and Liam Livingstone (33) took them to 139-5 in the 18th over.

But, with England needing 14 off the last over, Brook chipped a slower ball from fast bowler Nortje and South Africa captain Aiden Markram held a brilliant diving catch over his shoulder as he ran back from mid-off to end a 37-ball innings featuring seven fours.

Two balls later, Sam Curran struck a four but then refused a single, as that would have left lower-order batsman Jofra Archer on strike.

England now needed nine off two balls but Curran could only manage a single, leaving Archer with an impossible task off the final ball as England finished on 156-6.

It was a fine display under pressure by South Africa, often accused of 'choking' at major events.

Earlier, the Proteas were well-placed at 92-1 after losing the toss, with De Kock hitting fast bowler Archer for 21 in the fourth over, including two sixes off successive balls.

De Kock, however, was brilliantly caught by leaping England captain and wicketkeeper Jos Buttler off Archer for 65 to end a 38-ball innings featuring four fours and four sixes.

England, however, thought they had dismissed De Kock for 58 only for the third umpire to rule Mark Wood had grassed a low catch in the deep -- a key decision in a tight game.

De Kock's exit sparked a collapse that saw South Africa lose three wickets for 21 runs, with the big-hitting Heinrich Klaasen brilliantly run out by Buttler's direct hit on the stumps at the non-striker's end.

But David Miller's rapid 43 helped take South Africa to 163-6 -- and that was just enough.