The tourists' bowling unit stepped up big time in the first Test victory at Lord's before the batting frailties were exposed by the hosts in the big defeat at Old Trafford last week.
The Proteas batting unit have only managed one half-century across three innings in the series so far - 76 by opener Sarel Erwee in the Lord's Test - and were bowled out for totals of 151 and 179 in Manchester.
"I think it's quite obvious we need to get some hundreds up top, which hasn't been the case for a while now," number three Keegan Petersen told reporters on Tuesday.
"I think the lower order have saved us a few times but I think it's quite evident the batters have to step up now and get a couple of big scores."
The 29-year-old Petersen has yet to reach the three-figure milestone after nine Test matches but has four fifties to his name.
The right-hander top-scored with 42 in the second innings of the second Test but knows he needs to convert when he gets a good start at the highest level.
"I hadn't had a lot of time at the crease before that, so I take any positive I can from that innings. Though it was not as fluent as I would have loved it to be, I always try my best to fight for the team," Petersen said.
"I think it's all mental, it's getting starts but then getting out that is a problem for us.
"At least try to fight through that dark period and that's where you're going have to challenge yourself mentally all the time."