South Africa captain Mignon du Preez put Sri Lanka in after winning the toss and had every reason to feel vindicated as the home side slumped to 34 for six wickets inside 12 overs.
Pace bowler Susan Benade (2-7) and leg-spinner Dane van Neikerk (2-9) wrecked the Sri Lankan top order before South Africa's sharp fielding was rewarded with five runs outs as Sri Lanka were dismissed for just 79 runs in 20 overs.
Only two Sri Lankans - Dilani Manodara (24) and Chamani Seneviratna (14) - reached double figures in the match played at the Galle International Stadium.
Wicket-keeper Chetty was involved in six of the dismissals, including four runs outs, one catch and a stumping.
She returned to hit a 40-ball 33 as South Africa chased down the target in 17.2 overs, losing four wickets in the process.
South Africa play New Zealand in their next pool match on Friday at Galle while Sri Lanka play West Indies in the double-header on the same day.
West Indies opened their account meanwhile with a seven-wicket win over a formidable New Zealand side in Galle.
Chasing 118 for victory, West Indies was in trouble at five for two in two overs, with Tremayne Smartt and Shanel Daley both dismissed for ducks. It took the calm influence of Stafanie Taylor to steady the innings and bring some direction and purpose to the chase.
Taylor, who recently won the ICC Women's ODI Cricketer of the Year award, proved why she is considered one of the best in the game.
She stitched together a crucial 82-run stand for the third wicket with Deandra Dottin, before being trapped in front of the stumps for 35 by Sophie Devine, who struck with her first delivery to give New Zealand an outside chance.
However, Dottin didn’t lose her focus, and she soon brought up her fifth T20I fifty off just 36 balls. She struck six fours and two sixes to finish on 58 not out as her side achieved victory with seven wickets and 12 balls to spare.
Earlier, West Indies opted to bowl first and restricted New Zealand to 117 for nine in 20 overs, thanks to some outstanding ground fielding and catching.
New Zealand was given a swift start by captain Suzie Bates and Amy Satterthwaite, who put on 37 runs for the opening wicket in under five overs.
However, Aguilleira’s decision to introduce spin turned out to be a masterstroke, as she struck in her first over to dismiss Satterthwaite.
Sophie Devine (11) and Frances Mackay (2) departed in quick succession and New Zealand slipped from 63 for one to 66 for three in the 11th over.
When Bates was dismissed in the 17th over after a well-crafted 32, New Zealand was by no means in a safe position at 91 for 6. It lost a further three wickets to finish with a hard-fought 117 for nine.
For West Indies, Taylor, Anisa Mohammed and Shemaine Campbelle picked up two wickets apiece, and Deandra Dottin was named Player of the Match.
Group A is made up of Australia, England, India and Pakistan in the eight-team tournament being played in conjunction with the men's World Twenty20 tournament, also in Sri Lanka.
The top two teams from each group will qualify for the semi-finals, which will be played on the same day and at the same venue as the men’s semi-finals in Colombo on October 4/5 with the final to be played ahead of the men’s final at R.Premadasa Stadium on October 7.