Rickelton was brought into the team after Wiaan Mulder's injury in last week's first-Test win ruled him out, and he took his chance superbly on Thursday after surviving a massive scare on 98.
The 28-year-old, playing in his eighth Test, was adjudged leg before to a delivery that nipped back from Vishwa Fernando but was spared when a review of the umpire's decision showed a slight inside edge before the ball hit the pads.
Rickelton took a chance on reviewing the decision.
"I thought I was out. I'm still not sure I hit it at all, in all honesty," he said.
"I think I might have got lucky with some scratches. I wasn't reviewing for the ultra edge, I was reviewing because I was on 98, and because I was hoping the ball was maybe outside the line but I didn't feel anything."
But the snickometer showed a feint edge off the bat and Rickelton was given a reprieve, going on to reach 100 two balls later.
"It was more relief than anything else," he said of getting to three figures off 231 balls, to his obvious relief and the delight of the St George's Park crowd.
But he added only one more run before being dismissed when snagged by Pathum Nissanka at gully off Lahiru Kumara minutes before stumps.
Sri Lanka came back strongly after taking the second new ball and also dismissed Marco Jansen for four with the last ball before the close.
The home side had looked to have the upper hand as captain Temba Bavuma chimed in with 78 while Kyle Verreynne was 48 not out at the close and will resume on Friday along Keshav Maharaj.
Sri Lanka had the hosts in difficulty at 3-82 at lunch but Bavuma and Rickelton fought back and put on 133 for the fourth wicket before the skipper was dismissed in the penultimate over before tea.
He was tempted into taking on a series of short balls, eventually gloving a swing to Asitha Fernando's rising delivery and giving away his wicket when looking well set to go on and reach three figures. Bavuma has now made 23 Test fifties but only gone on to a century three times.
David Bedingham followed cheaply for six despite being handed two lives when he was dropped twice after top edging rising deliveries high into the sky.
But he continued an aggressive approach and was bowled by spinner Prabath Jayasuriya, dancing down the wicket and missing a wild swing at the ball.
Before lunch, Kumara took his 100th Test wicket as he bowled opener Aiden Markram for 20 and followed that up with the dismissal of home favourite Tristan Stubbs, who was caught behind for four runs.
Tony de Zorzi's was the first wicket to fall as he was dismissed first ball, trapped leg before wicket by Asitha Fernando at the start of the second over of the day.
Both countries are looking for victory to stay on track for a place in next year's World Test Championship final.
South Africa won last week's opening Test in Durban by 233 runs.
23°C