Mendis (76), Asalanka (79) & Shanaka (68) hit defiant, rapid fifties
But Sri Lanka are eventually bowled out for 326 to lose by 102 runs
South Africa post 428-5 - highest total in World Cup history
Markram smacks century off 49 balls - fastest in Men's World Cups - before falling for 106
Van der Dussen and De Kock also hit sublime centuries
Dilshan Madushanka steps up to deliver the final over of this innings, no doubt with some trepidation.
He starts with a dot and wide, before David Miller takes a big step back to guide the ball through backward point for four.
Steven Finn
Former England bowler on BBC Test Match Special
South Africa didn't really take risks as they laid a foundation early in the innings but it's been brutal hitting ever since.
Henry Moeran
BBC Test Match Special commentator
What a performance and statement from South Africa.
SA 419-5
Another six, and that's the World Cup record downed!
Marco Jansen sends it way, way over long-off and South Africa have reached the highest World Cup score with an over to spare.
Kasun Rajitha is struggling to find his line as he desperately searches for a delivery that's not going to be lashed to the ropes.
He delivers successive wides before landing a legitimate delivery and guess what? Miller crashes it for six.
Australia's 417-6 against Afghanistan in Perth in 2015 is the highest score made in a Cricket World Cup match.
Will South Africa break another record in Delhi?
400 up for South Africa, and of course it's done with a six!
A huge heave from Miller over mid-wicket, punishing Kasun Rajitha.
David Miller has mostly played spectator since coming in, but he gets into the action now.
Dilshan Madushanka delivers a no ball full toss that Miller dispatches to the ropes behind square, before driving down the ground for four more.
Henry Moeran
BBC Test Match Special commentator
That was rather clothed down the ground by Aiden Markram but his day's work included the fastest century in Cricket World Cup history so he should not be too downhearted.
Alex Hartley
Former England bowler on BBC Test Match Special
Aiden Markram could have hit that ball anywhere but had picked up the man right down the ground. A great innings.
Markram c Rajitha b Madushanka 106 (SA 383-5)
The fastest World Cup centurion departs!
Like a number of his predecessors, he holes out in the deep - heaving Madushanka's full toss down the ground and into the hands of Kasun Rajitha.
Markram leaves with 106 off 54 balls. All-rounder Marco Jansen is next up.
Matheesha Pathirana has pulled it back a bit in his final two overs and he saves the indignity of going for 100 runs from his 10 overs, holding South African to seven from the over.
He finishes with figures of 1-95.
Alex Hartley
Former England bowler on BBC Test Match Special
It's been an innings of power and finesse from Aiden Markram. Brilliant to watch. He played along the floor at the start of his innings then started to accelerate. He's been unstoppable.
Henry Moeran
BBC Test Match Special commentator
Aiden Markram takes off his helmet, mops his brow and stands like a gladiator saluting the crowd.
SA 375-4
Aiden Markram's done it! And in style - with a pulled six to bring up his century off 49 deliveries. The fastest hundred in World Cup history!
He came on strike for the third ball of Dilshan Madushanka over and took two to move to 92, before smacking the Sri Lankan seamer through point four. He needed four to beat the record - why hit one of those when smash a six?
Is sight of that fastest century record slips away from Aiden Markram? Matheesha Pathirana delivers a better over, keeping the South African batters to ones and twos.
But Markram finds the ropes from the over's final delivery, manoeuvring the ball through backward point. He's on 90 from 46 balls - 10 off four required to equal the record, three to beat it.
Meanwhile, Sri Lanka are three overs behind the required rate, so they'll have to bring three fielders into the ring for the final three overs. Not what you want to be doing when you're facing these batters in this game state.
Ireland's Kevin O'Brien has scored the fastest century in the Cricket World Cup when he reached three figures off 50 balls against England in Bengaluru at the 2011 tournament.
Could Aiden Markram break it here?
Aiden Markram is just rattling along!
He moves to 84 from just 43 balls, sending a huge six over long-on before a missile fired flat over the outfield is cut off at point for a single.
Daniel Norcross
BBC Test Match Special commentator
It's a wicket that Sri Lanka will be happy to have got given how dangerous Heinrich Klaasen can be but South Africa still have plenty of power still out there now David Miller has come to the crease.
Klaasen c Shanaka b Rajitha 32 (SL 342-4)
Another wicket from the first ball of the over - Klaasen goes.
Just like Van Der Dussen, Heinrich Klaasen departs after a change of ends, lofting a Kasun Rajitha ball into the hands of Sri Lanka captain Dasun Shanaka at long-off.
And here comes David Miller.