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
Beautifully elegant strokeplay from Sadeera Samarawickrama, who shows his ability to score all around the clock.
Samarawickrama gives himself room and gracefully lofts Keshav Maharaj's fourth ball over extra cover for four and then slog sweeps the spinner's final delivery all along the carpet to the fence.
A reminder that Kusal Mendis has kept wicket for 50 overs before coming out to strike the ball like thias.
Kagiso Rabada has stem the tide of runs a little off the next over as Mendis and Sadeera Samarawickrama pick up four runs in singles.
Here's how Marcos Jansen dismissed Kusal Perera a little while ago.
Sadeera Samarawickrama gets in on the act as he wallops spinner Keshav Maharaj over the rope at deep mid-wicket. More height than distance, but it's just got enough on it.
Matthew Henry
BBC Sport in Delhi
And that is the biggest six of the lot. Aiden Markram’s record might stand for about an hour here.
Steven Finn
Former England bowler on BBC Test Match Special
Absolute monster. Rabada trying to keep him guessing, slower ball last time and now a short ball. Only around chest height, Mendis can get around it and send it into the night sky.
Kusal Mendis certainly knows his strongest shot as his explosive hitting continues with two more sixes off Kagiso Rabada.
The Sri Lanka batter helps the fourth ball of Rabada's over the boundary at fine leg before smearing another six off the final delivery flatter and squarer.
Mendis now has 72 off 34 balls. He couldn't break Aiden Markram's record for the fastest World Cup century set in the first innings, could he?
Here are the three sixes that Mendis took off Lungi Ngidi a little while ago.
Steven Finn
Former England bowler on BBC Test Match Special
Nipped back through the gate. Nails the bail on the right-side of the stump and it flies off towards deep third. A good response from Jansen.
Perera b Jansen 7 (SL 67-2)
Marco Jansen punches the air.
The left-armer is able to beat the defence of Sri Lanka opener Kusal Perera, who sees the ball jag back and it beaten his bat and pad.
Incisive bowling from the South African.
In case you missed it...Aiden Markram broke the record for the fastest century in the Cricket World Cup in South Africa's innings.
Kusal Mendis has a better strikerate - 196.55 - than the South African at the moment.
Matthew Henry
BBC Sport in Delhi
This is undoubtedly the best atmosphere of the tournament so far.
Keystone Kops from South Africa in the field as Kusal Perera slices a delivery from Kagiso Rabada into the air between two fielders in the covers.
South Africa skipper Temba Bavuma and David Miller stare at each other as indecision gets the better of both men. Bavuma belatedly makes his move but he is unable make up his ground to take the catch.
That should have been a bread and butter take.
Steven Finn
Former England bowler on BBC Test Match Special
Semi-brainless bowling from Jansen, swinging in to a bowler who loves to play it off his legs and with mid-wicket up.
The joy of six for Kusal Mendis as he brings up his half-century off 25 balls.
Two sixes off Marco Jansen's latest over. For the first Mendis fetches it from outside off stump and heaves it across the line.
From Jansen's penultimate ball he sticks to his strongest shot, and again wallops it over deep square leg.
South Africa do not know where to bowl to him at the moment.
Daniel Norcross
BBC Test Match Special commentator
"Don't bowl there, son," I believe Ian Bell would say.
Kusal Mendis is definitely going to give this a crack, in fact.
The Sri Lanka batter takes back-to-back sixes off Lungi Ngidi to finish the over, twice heaving the seamer over the square-leg boundary for six.
Daniel Norcross
BBC Test Match Special commentator
That's gone a long, long way. No more than a little flick.
Kusal Mendis is going to give this a bit of a crack, you feel.
South Africa seamwer Lungi Ngidi is fractionally down leg side and the Sri Lanka batter uses the pace, with expert timing, to nonchalantly flick the ball over the boundary for six.
Here's how Marco Jansen claimed the wicket of Pathum Nissanka a few moments ago.
Daniel Norcross
BBC Test Match Special commentator
That flew off the bat. A marvelous shot.
Wide from Marco Jansen and Kusal Mendis chases it, slashing the ball high over the fielder a point to go for six. A bit of an uncompromising slice from Mendis but effective.