South Africa elected to bowl first and restricted West Indies to 176 for eight in their 20 overs, before easily chasing the target with the loss of one wicket.
It was another commanding performance from the South Africans following their 76-run win over India at the weekend, while the West Indies now face a likely must-win ‘quarter-final’ against the co-hosts Sunday.
India must still play Zimbabwe later on Thursday but assuming they win will be level on points with West Indies.
The only way South Africa can be denied a semi-final place will be if Zimbabwe win their last two games against India and Markram's side, and West Indies beat India in their final game to leave the latter two and South Africa on four points. But even then net run-rate should see the Proteas through.
South Africa tore through the West Indies top order with the ball, reducing their rivals to 83-7 before a brilliant record partnership of 89 for the eighth wicket between Jason Holder (49 from 31 balls) and Romario Shepherd (52 from 37 balls) gave the islanders a respectable total.
It still felt a little below par on an excellent batting wicket, and why the West Indies went so hard at the bowling up front with some reckless stroke making is unclear, but Holder and Shepherd showed at the back end how measured hitting was still hugely effective.
“I thought we bowled nicely," Markram said. "A team like West Indies will take the game to you. The pitch was tacky and 'stoppy'. With the early nip, we wanted to keep the ball up. The steep bounce came from the tackiness.
"Fortunately we ended up on the right side of the toss. A lot of credit to the bowlers. It felt like while we were bowling, the wicket kept getting better and better. Towards the back end, when we went full and yorkers and change of pace, it didn't work."
Wily seamer Lungi Ngidi was again excellent with the ball as he returned figures of 3-30 in four overs, while Kagiso Rabada had his best spell of the tournament for 2-22 in four.
South Africa went hard from the start but unlike West Indies played proper cricket strokes as Markram and fellow opener Quinton de Kock (47 from 24 balls) put on 95 in 48 balls with some controlled power hitting.
Ryan Rickelton came in at the departure of De Kock and smashed an unbeaten 45 in 28 deliveries as South Africa cantered to victory.
"Ricks (Rickelton) has come and made No. 3 his own," Markram said. "No step in this competition is easy. Hopefully we get through (to the semifinals). Will be great, we don't think too far ahead but boys have got used to the conditions here."
