|First one-day international, Cape Town|
|England 258-8 (50 overs): Denly 87, Woakes 40; Shamsi 3-38|
|South Africa 259-3 (47.4 overs): De Kock 107, Bavuma 98|
|South Africa won by seven wickets|
World champions England were "way off the mark" in their heavy seven-wicket one-day international defeat by South Africa, said captain Eoin Morgan.
Quinton de Kock hit 107 and Temba Bavuma 98 as the hosts chased down England's 258-8 with 14 balls left.
The pair combined for a partnership of 173 and made the tourists' under-strength attack look toothless in their first ODI since winning the World Cup.
England's top order also failed, falling to 131-6 before Joe Denly's 87.
Denly's innings looked to have kept England in the game, but De Kock and Bavuma were ruthless where England's batsmen were not.
De Kock was eventually bowled trying to slog-sweep Joe Root and Bavuma fell agonisingly short of a second ODI hundred when he was trapped lbw by a ball that skidded on from Chris Jordan.
Those wickets slowed South Africa's victory push but they were always in control of the chase with Rassie van der Dussen scoring 38 not out.
"Right from the beginning of our innings, we struggled to adapt to the conditions," Morgan told the Test Match Special podcast.
"We did our best to adapt but the skill level wasn't there.
"We'll identify the little reasons why we didn't gel as a team today because if we play like that again, we'll lose."
England, who have rested a handful of their World Cup winners for this series, now trail 1-0 in the three-match contest and face the prospect of losing an ODI series for the first time in three years.
England's second-string attack dominated by Proteas
It is 205 days since the greatest day in England's white-ball history, when they beat New Zealand at Lord's to win the men's World Cup for the first time. This defeat was as chastening as anything seen in recent years in a period when Eoin Morgan's side have usually dominated.
England's total proved to be well below par and the bowlers were punished comprehensively by De Kock and Bavuma.
England badly missed the pace of Jofra Archer and Mark Wood, who were both rested for the series, and were lacking the guile provided by Liam Plunkett and Adil Rashid in the middle overs. Plunkett has been dispensed with since the World Cup while Rashid is on the tour of South Africa but was not selected.
Chris Woakes, the only member of the World Cup final bowling attack to feature, was economical with the new ball and had opener Reeza Hendricks caught behind in the seventh over but the other bowlers struggled.
Sam Curran shared the new ball and was not threatening, while Tom Curran and Chris Jordan looked one-paced and were wayward for the majority.
Leg-spinner Matt Parkinson, making his ODI debut, was largely anonymous as the sole frontline spinner, going wicketless in 8.4 overs.
De Kock and Bavuma were patient early on but rotated the strike well and as the partnership grew, the pair made the most of the increasing number of opportunities they were given by the bowlers.
De Kock, playing in his first ODI since being appointed captain, compiled a mature innings that was not overly attacking. He hit boundaries all around the wicket, including an emphatic six back over Tom Curran's head and a fine cover drive off Parkinson that took him to his 15th ODI century.
Bavuma was arguably even more impressive, scoring at ease throughout, and deserved to reach three figures.
World Cup winners fail with the bat
In addition to England's weakened bowling attack, World Cup winners Ben Stokes and Jos Buttler - both rested - were absent from the batting line-up.
Openers Jonny Bairstow and Jason Roy, plus Joe Root and Eoin Morgan, did feature and were all part of the top-order failure.
Roy and Bairstow had made a promising start by reaching 51-0 but were out in consecutive overs, mistiming aggressive shots to long-on and mid-off respectively as they perhaps aimed for too high a total too early.
Root and Morgan steadied England with a partnership of 30, but Root was brilliantly run out by a direct hit from Van der Dussen and Morgan edged left-arm wrist-spinner Tabraiz Shamsi to slip for 11 three balls later.
After their good start, England were quickly bogged down by South Africa's seamers' slower balls and the spin of Shamsi and JJ Smuts.
Debutant Tom Banton, the highly-rated 21-year-old batsman, showed glimpses of his promise with three boundaries - a reverse sweep, a powerful pull and a fine straight drive - but was trapped lbw for 18.
When Sam Curran was bowled around his legs in the 28th over, it looked like England would not bat out their 50 overs.
At the age of 33, Denly is a curious selection in this team as England build for the Twenty20 World Cup in October and their defence of the 50-over World Cup in 2023, but he and Woakes (40) were the only batsmen to look confident.
Denly was circumspect early on before scoring 51 off his final 39 balls, but his intelligent innings was ultimately in vain.
"For us, plans B and C are when we come up on wickets like this and should adapt, manipulate what we're trying to do, and the projected total comes way down to 275 or 300," Morgan said.
"We [Morgan and Root] spoke about that while we were in the middle but weren't good enough to implement it today.
"You watch guys like Jason Roy and Jonny Bairstow crunching the ball and it can lead to a misconception that the wicket is better than it actually is.
"If you actually look at the way they hit the ball, they were hitting it in the air off the ground whereas normally they drill the ball along the ground. Balls that they smashed didn't go for six.
"Little indications like that should drip into the changing room."
Analysis - England 'strangely flat'
BBC Radio 5 Live's Simon Mann in Cape Town
The T20 World Cup in Australia in October and November is England's next white-ball priority so only five of England's World Cup-winning side featured on Tuesday.
Few of England's back-up players advanced their cause in a strangely flat performance.
Joe Denly, with his first ODI fifty for more than a decade, gave England something to defend, but the bowling attack looked toothless.
Quinton de Kock has shown throughout the South African summer that he's the class player in this line-up, and he was superb again.
Perhaps South Africa sensed it was going to be their day when Rassie van der Dussen produced a stunning piece of fielding to run out Joe Root - arguably the decisive moment in England's innings.
'Responsibility of captaincy helped me'
South Africa captain and man of the match Quinton de Kock: "It was a good night. We're just glad to get a win under our belts, it feels good to get back to winning ways.
"This week we've had one or two chats about how we wanted to take this ODI side forward, today was a good start. It's alright talking but to bring it out to the field I'm really pleased about.
"To be honest I did feel the weight of captaincy while I was batting. I enjoyed it, it kept me in the game. That extra bit of responsibility helped me."