The benchmark JSE Top40 index inched up 0.04 percent to 46170.1 points, while the broader all share index dropped 0.14 percent to 52918.42 points.
The banking index retreated 1.78 percent to 6820.98 points, its biggest daily loss since December 2015 when President Jacob Zuma changed finance ministers twice in a week.
“What usually happens is that hedge funds have mandates when things get downgraded to junk ... to de-leverage or sell out because they are not allowed to hold risky debt on their books,” BP Bernstein trader, Vasili Tirasis, said.
Capitec Bank weakened 4.85 percent to R720, FirstRand fell 0.82 percent at R44.90, Standard Bank retreated 1.64 percent to R136.47 and Nedbank declined 1.35 percent to close at R225.80.
Read also: S&P downgrades SA banks
Meanwhile, US stocks rose in early trading, led by energy companies and a rebound in financials.
The Dow Jones industrial average was up 0.23 percent at 20695.32 points, while the Standard & Poor’s 500 rose 0.25 percent at 2358.81 points.