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
Alex Hartley
Former England bowler on BBC Test Match Special
Rassie van der Dussen has shown great patience. He showed if you stick around and put in the hard yards you get the reward. Quinton de Kock catches your eye with the way he strikes the ball but Van der Dussen has a very simple approach.
There's that century for Rassie van der Dussen!
He had to wait a few overs after he moved to 96 with a big six, working a couple of singles to move to 98.
He takes a single from the first ball of Dasun Shanaka's over, and having returned to the striker's end is greeted by a slower ball. He has to adjust a bit, but is able to work the ball down the ground for a single and his century, which comes off 103 balls.
Maybe Aiden Markram fancies beating Van der Dussen to that century? A single brings the new batter on strike and he sets about putting Dilshan Madushanka away.
He starts with two more cracking drives down the ground, the second so bullet fast that Van der Dussen has to star jump to get out of the way. A third four comes from a smart pull, and Markram moves to 21.
Bangladesh cruised to a six-wicket victory over Afghanistan to begin their World Cup campaign in Dharamsala.
Afghanistan batted first on a good pitch but squandered the opportunity as they were bowled out in a haze of loose strokes for 156 in 37.2 overs.
The Tigers were 27-2 in reply, but a stand of 97 between Mehidy Hasan and Najmul Hossain Shanto helped them reach their target with 15.2 overs to spare.
Bangladesh next meet England at the same venue on Tuesday (06:00 BST).
Matthew Henry
BBC Sport in Delhi
Australia's 417-6 against Afghanistan in Perth in 2015 is the highest total in a World Cup, by the way. That's under major threat today.
Sri Lankan captain Dasun Shanaka brings himself back into the attack. It's a solid over, somewhat spoilt by the final ball as Markram plays a gorgeous drive for four.
Just a single for Van der Dussen from the over, he's moved to 97.
Alex Hartley
Former England bowler on BBC Test Match Special
Fresh legs at the crease for South Africa with Aiden Markram so that will bring energy to take ones and twos.
A quiet little over from Dunith Wellalage after all the excitement at the other end.
Just four off it, Markram picking up three of them with the other a wide.
Are we in the eye of the storm?
Aiden Markram ventures to the crease with this South African side well set for a big total.
He'll be eyeing the boundaries, but has to settle for a single to get going as squeezes the ball into the covers.
Matthew Henry
BBC Sport in Delhi
I was just about to say how special the atmosphere was when De Kock got to his hundred. Chants of "Quin-ton! Quin-ton" were going around this stadium.
De Kock c de Silva b Pathirana 100 (SA 214-2)
Quinton de Kock has maybe got a little giddy after reaching three figures. A ball later and he's on his way back to the pavilion.
It's dug in short by Matheesha Pathirana and the South African left-handed opener balloons it up into the leg side as he attempts to whip it.
Dhananjaya de Silva, on the move, jogs in and calmly pouches the catch.
De Kock looks furious with himself and is given a hug by Rassie van der Dussen.
Daniel Norcross
BBC Test Match Special commentator
Quinton de Kock has got to three figures in style. It's been a really good knock.
A century for Quinton de Kock!
He saw Rassie van der Dussen accelerating towards his hundred in the previous over and decided he'd get there first.
An edge off Matheesha Pathirana brings four and the 200 partnership, before smashing the ball through mid-wicket to bring up the hundred off just 83 balls.
Cracking stuff.
Russel Arnold
Former Sri Lanka all-rounder on BBC Test Match Special
A lot of the South African players have been in the IPL. They have used their experience of playing in India to take their game to a different level when playing international cricket.
Van der Dussen moves into the 90s and brings up the South African 200 with a reverse sweep off Dunith Wellalage that finds the ropes. He then lofts the Sri Lankan bowler for a big six over square. That went very far.
206 runs from 30 overs. The old formula is you try and double your score from this point - and you'd fancy South Africa to do so.
Matthew Henry
BBC Sport in Delhi
They have brought two chairs out as well as umbrellas for the South Africa batters during drinks.
Jonathan Agnew
BBC cricket correspondent on Test Match Special
This is a disastrous over for Sri Lanka. A missed run out, five wides and now De Kock has stuck one into the stands.
Matheesha Pathirana has returned to the Sri Lankan attack and after the early excitement of that run-out chance he offers up a wild set of deliveries.
His second ball flies way, way wide and races away for five runs, before De Kock heaves him over fine leg for six. Another wide follows, before the over finishes somewhat more sedately with two singles.
Jonathan Agnew
BBC cricket correspondent on Test Match Special
He's thrown to the wrong end! Actually - De Kock didn't have his bat back either. He was very slack.
Oh wow! Almost a run-out, that would have been an embarrassing way to end this fine partnership.
Quinton de Kock thinks of running a ball to gully as Van der Dussen advances for a quick single. The batter on strike sends his partner back but is slack turning back, the ball is thrown in on the dive and only just misses the base of the stump.