Teenager Vishmi Gunarathne was hailed as Sri Lanka's "young superstar" after helping her side to a shock three-run win over South Africa in the opening match of the Women's T20 World Cup.

The 17-year-old, playing in only her 10th international in the sport's shortest format, hit a composed and fluent 35 off 34 balls as Sri Lanka posted 129-4 batting first at Newlands on Friday.

South Africa finished on 126-9 in their 20 overs.

Gunarathne played her part in a crucial 86-run second wicket partnership with skipper Chamari Athapaththu who saluted her teenage teammate.

"Vishmi is the young superstar of our team. Her attitude is exactly what I want to see and she handled the fast bowlers very well," said Athapaththu who made 68 off 50 balls opening the innings.

"She has a very bright future."

Gunarathne is used to South African conditions having captained Sri Lanka at the recent Women's Under-19 World Cup in the country.

She also showed no sign of the back stress injury which forced her to sit out the Asian Cup in Bangladesh five months ago.

Friday's match was Sri Lanka's first competitive T20 international since that tournament in October.

"We have a good culture in the team, a lot of youngsters and the senior players share knowledge with them," added Athapaththu.

"We all know South Africa are one of the best teams in the world and they are playing in their home conditions. But we played good cricket and we won."

Sri Lanka have never progressed past the first round of the T20 World Cup in seven campaigns.

Athapaththu, 33, who has played in all of those World Cups, says her team will not fear their next opponents Bangladesh who they face on Sunday.

"We have upset some big teams a few times, and we've done it again. This time we will try to play good cricket and go to the semi-finals, that's our aim," added the captain.

"We don't fear any team. The rankings are just a number."

After Bangladesh, the Sri Lankans face New Zealand as well as defending champions Australia in Group A.

The top two sides from each of the five-team pools progress to the semi-finals.