Bethell was one of the bowlers to restrict South Africa to 209 all out before hitting 88 to see England set up a clash with either Sri Lanka or Afghanistan.
South Africa endured a slow start having won the toss and chosen to bat, their first boundary came off the final ball of the fourth over, before Joshua Boyden dismissed Valentine Kitime off the next delivery.
Boyden would claim his 12th wicket of the tournament to send the other opener Ethan-John Cunningham back to the hutch and reduce South Africa to 21 for two.
Dewald Brevis and Gerhardus Maree combined to steady the South African ship, adding 55 runs to the total before Bethell dismissed Maree.
England are through to the first Super League semi-final of the #U19CWC 2022 🎉They defeat South Africa by six wic… https://t.co/AgBKP3pXnm
— Cricket World Cup (@cricketworldcup) 1643222273000
Brevis remained a familiar stronghold for South Africa as he brought up his fourth fifty-plus score in a row eventually falling just short of a century on 97.
His dismissal brought about a batting collapse for South Africa as three wickets fell for one run as the batters went in search of boundaries, but only found the grateful hands of fielders with Rehan Ahmed claiming figures of four for 48.
The final-wicket partnership of Matthew Boast and Asakhe Tsaka frustrated England adding 40?runs as South Africa ended on 209 all out.
Bethell came out all guns blazing in England’s chase, hitting the fourth fastest half-century of U19 World Cup history, reaching fifty off just 20 balls, as the Young Lions went at over 10 an over.
George Thomas was a delighted onlooker at the non-striker’s end only moving into double figures in the tenth over, before smacking a six to bring up England’s hundred.
South Africa finally struck as Bethell went for one heave too many but not before he had put on 88 from 42 deliveries to place England as overwhelming favourites.
That tag was backed up by good partnerships in the top order, before William Luxton came in at five to strike 47 from 41 balls and get England into the semi-finals with a six.
ZIMBABWE, WEST INDIES WIN IN THE PLATE COMPETITION
Matthew Welch’s 78 helped Zimbabwe set Scotland a tricky chase of 249 in their Plate quarterfinal.
Matthew Nandu 💯#WIvPNG | #U19CWC https://t.co/YakQXT6glI
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Scotland were unable to build partnerships as they slumped to 140 all out to see Zimbabwe advance to meet Ireland.
🔹 54 runs from 58 balls🔹 Five fours and a sixA resilient knock from Zimbabwe’s Brian Bennett against Scotland in… https://t.co/68Mvdqb9p6
— Cricket World Cup (@cricketworldcup) 1643209630000
They will be joined in the semifinals by hosts West Indies who were too good for Papua New Guinea in a 169-run win.
The West Indies will now face the United Arab Emirates, while Papua New Guinea are set to take on Uganda in the Plate play-offs.