NAGPUR: In-form West Indies continued their unbeaten run and defeated South Africa by three wickets to seal their spot in the semi-finals of the ICC World Twenty20 on Friday.With three wins out of as many games, West Indies thus became the second team after New Zealand to enter the semi-finals of the marquee event.South Africa are virtually out of the tournament and their fate now hinges on the result of Saturday's Super 10 Group 1 match against England and Sri Lanka at New Delhi.If England win tomorrow, Eoin Morgan's men will secure their place in the semi-finals as the second team from Group 1 and the match between South Africa and Sri Lanka will be a mere formality.Electing to bowl, West Indies first restricted South Africa to 122 for eight and then chased down the target with two balls to spare with three wickets in hand.Chasing 123 for win, West Indies were dealt a severe blow in the fifth ball of their innings when dangerous Chris Gayle was cleaned up by a late in-swinging delivery from Kagiso Rabada.Johnson Charles (32) took the offensive to the opposition, hitting Chris Morris for two boundaries to pick up 11 runs of the fourth over.Known for their fielding prowess, South Africa stayed on in the contest, courtesy a brilliant effort from Rilee Rossouw whose's direct throw on to the stumps caught Andre Fletcher (11) short of the crease.Charles carried on his good work in the company of Marlon Samuels (44) before the former went for a huge swipe only to give a skier to South Africa captain Faf du Plessis at cover.But Rabada's next over eased the pressure for West Indies as he went for three boundaries -- one by Dwyane Bravo and two by Samuels.Bravo, however, departed in the last delivery of the next over handing a simple catch to Wiese at backward point off Aaron Phangiso while going for a wild slash outside off-stump.With West Indies needing a manageable 24 off 24 balls, it took a superb 17th over from leg-spinner Imran Tahir (2/13) to bring South Africa back into the match.After dropping a difficult chance from Samuels off his own bowling, Tahir came back strongly and picked up two wickets in consecutive balls to the delight of the Proteas.Tahir first dismissed Russell as the batsman went for a huge slog across the line only to find Miller at deep midwicket and then castled West Indies skipper Darren Sammy with a first ball googly.Needing 20 off the last two overs, Samuels struck Wiese for two boundaries to bring down the equation to 10 off eight before a rash shot from the right-hander found AB de Villiers at long-on.With West Indies requiring nine off the last over, Carlos Brathwaite (10 not out) clobbered a length delivery from Rabada over the midwicket boundary to bring down the equations to three off four balls, which they accumulated with consummate ease.Earlier, it was struggle for South Africa from the word go as they lost wickets at regular intervals and failed to put on a substantial partnership to get to a wining total.Despite having some many big hitting batsmen in their ranks, the Proteas could only hit eight boundaries and two sixes in their entire 20 overs.Left-handed opener Quinton de Kock top-scored for South Africa with a 46-ball 47, while Wiese made a valuable 28 lower down the order.Sent into bat, South Africa were in dire-straits, losing their first five wickets inside the 50-run mark.Hashim Amla became victim of a terrible mix up in the third delivery of the match, while skipper Faf du Plessis (9) was brilliantly holed out by Suleiman Benn at mid-off off Andre Russell in the last ball of the second over, soon after the right-hander clobbered Russell over mid-off two deliveries earlier.Rossouw was the next to depart for a duck, cutting a Gayle delivery straight to Russell at point as South Africa slumped to 20 for three in three overs.Much was expected of De Villiers (10) but he too perished in the eight over after being completely foxed by a slower delivery from Bravo.While going for an outrageous flick through midwicket, De Villiers got a thick inside edge straight onto his stumps, much to the disappointment of the capacity crowd.If that was not enough, Gayle went through another dangerman David Miller's defence to see South Africa in a spot of bother at 47 for five.De Kock and Wiese then held the innings together with a crucial 40-run stand for the sixth wicket to take South Africa forward.But just when it seemed things were starting to look bright for South Africa, De Kock, on whom South Africa depended much to get to a fighting total, perished after doing all the hard work. He was bowled by Russell as the left-hander went for an injudicious sweep to a full ball bowled around his legs.In search of big shots, Wiese then skied a slower delivery from Bravo to West Indies skipper Sammy at mid-off.For West Indies, Gayle (2/17), Bravo (2/200 and Russell (2/28) picked up two wickets apiece.