Seventeen-year-old Capsi (25 off 17) hit four consecutive boundaries in the second over after being promoted to number 3, while Ecclestone scored 33 off 12 balls, hitting two sixes and three fours. A 26-run final over England posted 176-6 in the derby to make a 3-0 T20I sweep.
Capsi’s fellow 17-year-old Kemp (2-18) was then stumped by Amy Jones to Anneke Bosch (17), the latter to dismiss the Proteas’ top scorer Tamzin Britts (59 off 57) as South Africa 138- Got out on 6.
Capsi once opened the game in the Powerplay when opener Sophia Dunkley (0) was struck off the first ball of the match by Nonculleko Mlaba (3-22) after England stand-in captain Nat Sciver was elected to bat.
Playing only the second game for her country, making her debut in Worcester on Saturday, she showed class, hitting four fours through mid-on, backward point, extra-cover and backward square.
Capsi tried another boundary off left-arm spinner Mlaba at mid-off but stand-in captain Chloe Tryon took a brilliant catch.
Issie Wong’s in-swinger bowled left-armer Lara Goodall (2) in the first over of South Africa’s innings, but Bosch and the Brits put on a 54-run second wicket partnership to keep the match going.
Left-handed Kemp broke the deadly partnership stand in the ninth over before dismissing the Brits in the 18th as Ecclestone smacked a catch at deep midwicket.
Spinners Ecclestone and Sarah Glenn were the other England bowlers to strike in the evening – Ecclestone’s 2-24 which also included Tryon’s wicket for 14 off the final ball of the game.