South African wicketkeeper-batsman Rickelton scored his third test century on Friday to go with Wiaan Mulder's 115 as the home side set Australia a daunting 288 for victory on a deteriorating wicket on the final day.
Adding to tourist's task is the fact that scoring with the older ball is hard.
"It definitely felt quite slow, and when the ball was soft it was difficult to beat the infield,” Rickelton told reporters at the close of the fourth day. "With the new ball, there are runs available, but there are wickets available as well.
"The bounce was a little two-paced, although we didn't see too many balls staying low, unfortunately from our point of view.
"I think it's going to be a grind. For Australia to score at three runs an over throughout the day would be a big ask on a slower, lower and deteriorating wicket."
Harmer will be key to the South Africa's chances with rough patches outside the off-stump for the right-handers.
"It was a lot easier for me as a left-hander because there wasn't much turn from the straight areas of the pitch,” Rickelton said.
"When the off-spinner went wider and bowled into the rough, trying to lure me into playing outside off stump, there was a much greater chance of an edge or a dismissal.
"I'm actually surprised there isn't more turn from the straight, considering the (hot) weather we've had in Cape Town over the last few days. For the right-handers, though, that ball turning back in can be vicious.”
The series is level at 1-1 after Australia won the first test in Durban and South Africa bounced back in Gqeberha.
"It's been a special series. It's ebbed and flowed across all three games,” Rickelton said. “Both teams have got ahead at different stages, only for the other to fight back. There have been mistakes and some really good cricket as well.
“Hopefully it comes down to a really good day for South Africa tomorrow.”