The Proteas managed just 175 before they were bowled out in the 39th over, a total that could have been much worse were it not for the unbeaten 56 from David Miller and the wagging tail of Rory Kleinveldt (43) in a stand of 95.
In-form James Anderson sent Colin Ingram back to the sheds at the Kia Oval before South Africa had scored a run, and it was mostly down hill from there as the English seamers made the most of the swinging ball in overcast conditions.
Hashim Amla went in the first over from the other end from Steven Finn for 1 before a bit of a stand from Robin Peterson (30), promoted to number three, and Faf du Plessis (26).
But South Africa fell to 4 for 50 as Anderson picked up Peterson LBW and skipper AB de Villiers went for a duck.
JP Duminy, who will replace Ricky Ponting as the international player at Surrey for the end of the county season, managed just 3 before he was bowled by James Tredwell.
The next three wickets fell for just 10 runs. Du Plessis went caught behind from man-of-the-match Tredwell, before Ryan McLaren was run out by Jonathan Trott and Christopher Morris also nicked into keeper Jos Butler’s gloves off the Kent spinner.
At eight for 80, it looked a done deal but for a rear-guard action from Miller and Kleinveldt.
“I’m very proud of [Miller and Kleinveldt],” de Villiers said on-field at the end of the game.”A lot of sides would have got bowled out for 100 there.”
“[We have] no excuses. I truly believe we had the talent to win this tournament. We’re bitterly disappointed. We just didn’t play well enough.”
England still had to get the runs and gave the tourists a sniff when captain Alastair Cook flashed at a short one and got caught behind off Morris for 6.
Ian Bell fell the same way, caught by keeper de Villiers, this time from bowler Kleinveldt, who came in for the injured Dale Steyn.
The only other wicket to fall was Joe Root for 48, but with his team on 146 the job was done.
Trott (82 not out) made no mistakes and was there when Eoin Morgan (15 not out) dispatched a full toss for four.
England now play the winner of the India or Sri Lanka semi-final in Cardiff tomorrow in the final on Sunday at Edgbaston in Birmingham.
Does Cook, who was criticised for letting South Africa off the hook with negative field placements and bowler choices, mind who they play? “Not at all,” he said. “Hopefully they can have a tight game and knock each other about a bit.”
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