Aiden Markram admitted South Africa rode their luck as they maintained their perfect record at the T20 World Cup with a tense four-run win over Bangladesh on Monday.

The Proteas looked to be heading for their first loss in Group D when they toiled to 113-6 in Long Island, but some slow scoring from Bangladesh left the match in the balance late on.

Requiring seven runs from the final three balls for victory, Bangladesh saw both Jaker Ali and Mahmudullah caught by Markram, who was in the right place at the right time on the boundary as South Africa's opponents went in search of a maximum.

The result keeps South Africa top of Group D and on course for a Super-8 berth with six points, four clear of Bangladesh, but Markram acknowledged they had been lucky.

"You're always pretty nervous in the final over in a game like that. It was always on a knife's edge, it can make you mentally tired," he said after the match.

"It's always nice to be in them though. Sometimes you get on the right side of it, sometimes not, but it's very entertaining. 

"That 19.5 full toss could've gone anywhere, it could've gone two more metres further and we'd have had a different conversation. 

"A few things went our way today, we were very fortunate to get on the right side.

"Today was one of those days where the seamers were bowling well, we wanted to drag it to the end where anything could happen in the last over."

Heinrich Klaasen hit a vital 46 to drag South Africa to 113 after they had been teetering on 23-4, putting up a 79-run partnership with David Miller, who hit 29.

"We're putting Klaasen and Miller under pressure but they've been exceptional," Markram added.

"They've gone back-to-back with crucial partnerships, got us to a score that was luckily enough to win but still one we could defend. It's fantastic for Klaasy to get back in form."