England slumped with the bat and then dropped Laura Wolvaardt twice as they slipped to a six-wicket loss to South Africa in the first one-day international at Kimberley.
England laboured to 186 all out on a sticky pitch after electing to bat, with No 8 Charlie Dean (47no off 57) top-scoring after South Africa all-rounder Marizanne Kapp - who had been rested for the T20 series that the hosts lost 3-0 - shredded the top order.
Kapp nicked off Sophia Dunkley (4) in the first over before removing Tammy Beaumont (11) and Nat Sciver-Brunt (0) in the seventh.
Captain Heather Knight - who would have been caught behind for eight had South Africa reviewed - scored 40 before England were indebted to Dean, who put on 67 from 64 balls with fellow spinner Sophie Ecclestone (17) from 106-7 at Diamond Oval.
Proteas captain Wolvaardt (59no off 114) was grassed on five and 27, by wicketkeeper Amy Jones and Dunkley at deep square leg respectively, and anchored the innings as the hosts reached their target with a whopping 70 balls to spare.
Nadine de Klerk (48no off 28) played a swashbuckling cameo at the death, hitting 11 boundaries and smoking all but five of the runs in a stand of 53 from 39 balls with Wolvaardt, including the winning four off Dean two balls into the 39th over.
South Africa will look to wrap up a series win with victory in Sunday's second game in Durban (8am UK) before the final ODI in Potchefstroom next Wednesday (12pm UK), both live on Sky Sports.
Kapp had Beaumont dropped on nought in the opening over by wicketkeeper Sinalo Jafta but Jafta atoned moments later to snaffle Dunkley as Kapp found the edge again.
Kapp was a constant threat in the powerplay and struck twice in four balls in the seventh over, uprooting Beaumont's off stump and then pinning Sciver-Brunt lbw on the back foot as the England vice-captain suffered just a fourth duck in 97 ODI innings.
Knight led a rebuild of sorts, after the hosts failed to detect an edge off Kapp in the fifth over, but England lost regular wickets at the other end, with Danni Wyatt-Hodge (11) burning the tourists' second review as she fell lbw and Jones (21) hauling to deep square leg.
The captain eventually departed at the start of the 26th over, lbw to spinner Nonkululeko Mlaba (2-47), four overs after Alice Capsey (8) had been trapped by the same bowler in the same fashion.
South Africa then lost their discipline in sapping heat, including with a series of wides, helping Dean and Ecclestone stitch a half-century stand before two Annerie Dercksen (3-16) wickets and the comedy run out of Lauren Bell (0) ended the innings.
Tazmin Brits (13) and Sune Luus (7) were out lbw in the chase, with their reviews scuppered by ball-tracking not working at that point; Luus' dismissal off Dean looked fair enough but Bell's ball to remove Brits - after the batter had struck three fours in an over off Lauren Filer - may have slid on past leg stump.
Filer and Bell were a little wayward with the new ball before Dean, Sciver-Brunt and Ecclestone dragged things back, but Wolvaardt punished the tourists for dropping her twice, scoring her 33rd ODI fifty, from 92 balls.
The dismissal of Dercksen (27), caught by Beaumont on the deep square leg boundary off the expensive Filer (1-45 from six overs) after putting on 59 with Wolvaardt for the third wicket, did not derail the Proteas, with Player of the Match Kapp (22 off 22) playing a punchy innings and De Klerk then dazzling at the end.
England captain Heather Knight:
"I'm obviously disappointed, but I think there were some positives. That partnership with Charlie [Dean] and Sophie [Ecclestone] gave us a chance of being in the game, but unfortunately we didn't quite have enough.
"We thought we were in the game. We probably searched for wickets a little bit too much because we felt we needed to bowl them out having only got 186 on the board ourselves.
"It felt really close, it felt like we were really in the game. A couple of wickets and we'd have been right in with a chance. Nadine [de Klerk] played a brilliant innings and they were able to take the game away at the back end."
South Africa skipper Laura Wolvaardt:
"The way we started was awesome. [Marizanne] Kapp was exceptional as always. It's nice to have her back, you can see what a difference she makes to our side.
"We were a little disappointed [England scored 186], but the seam just started dying out a little bit and it was tough for the bowlers in the heat.
"There was always going to be some fightback from England, they have a good line-up and bat deep, but I'm happy we held on and kept them under 200."
All times UK and Ireland; all games live on Sky Sports
