The Proteas bettered the previous World Cup best of 417 made by Australia against Afghanistan at Perth in 2015.
Their 428-5 was also the ninth highest total in all one-day internationals.
Markram, who went on to make 106, beat the record for fastest World Cup century set by Ireland's Kevin O'Brien off 50 balls against England at Bengaluru in 2011.
Rassie van der Dussen (108) and Quinton de Kock (100) also hit centuries in the first World Cup match to feature three tons in the same innings.
"It was a perfect day for us with the bat. We had to work hard up front up against the swinging ball and then well into the middle overs," said Van der Dussen.
"We have a blueprint to set it up for the guys in the middle order. Aiden Markram when he plays like that is incredible to watch."
For Sri Lanka, the figures made grim reading with bowlers Matheesha Pathirana (1-95) and Kasun Rajitha (1-90) conceding more than 180 runs from 20 overs.
