The rand slumped ahead of keenly-awaited US inflation data and a European Central Bank policy meeting as traders seek clues on the timing of higher interest rates that could hinder economic recovery.
On Wednesday evening, the rand was 1.6% weaker at R13.74.
The JSE's all share index ended the day flat at 67681 points.
Global equities have been in a holding pattern this month as traders try to determine the outlook for central banks' policies amid concerns that a spike in prices as economies emerge from lockdowns could raise borrowing costs.
Price inflation of goods leaving Chinese factories rose at the highest rate in more than a decade last month, official data showed, as the world's second-largest economy worked to contain a surge in commodity prices.
All eyes were now on US inflation figures due Thursday.
"The tight trading ranges seen so far this month reflect the cautious mood in the market ahead of the inflation numbers," said Fiona Cincotta of City Index.
"Whilst the Fed reassures that this spike in inflation is temporary, policy makers will need to be out in their droves to calm the market."
European stocks ended the day mostly lower.
Meanwhile US stocks were modestly higher in late morning trading, with the S&P 500 sitting near its record high.
"US stocks are mostly higher in early action as the S&P 500 gives another run at record highs ahead of highly-anticipated inflation data due out tomorrow," said analysts at Charles Schwab brokerage.
"Stocks have struggled to breakthrough to uncharted territory as of late as the markets grapple with signs of heating up economic activity and inflation pressures that have called into question when the Fed may begin to dial back its asset purchases," they added.
Thursday also sees the ECB's latest decision on policy, with analysts not expecting any changes but looking for shifts in its outlook as the recovery presses ahead.
"It's an opportune time for a thorough review given the improved state of both the economy and the vaccination rollout," said National Australia Bank analyst David de Garis.
"While there's no denying the better run of data... prudence around the pandemic, including from variants, also argues for a degree of policy caution."
Hopes for another bump in demand were given a boost after the United States eased a travel warning for dozens of countries including European nations and Japan as vaccinations allow people to return to a semblance of normality.
Markets were looking ahead also to the start Friday of a summit of the Group of Seven (G7) wealthy nations.
The gathering in England will be Joe Biden's first foreign trip as US president.
British Prime Minister Boris Johnson, host of the summit featuring leaders also from Canada, France, Germany, Italy and Japan, is set to urge the seven nations to vaccinate the whole world against coronavirus by the end of 2022.
The decision by El Salvador to make bitcoin legal tender, making the Central American country the first nation to adopt a cryptocurrency for everyday use, helped boost its price.
The price of bitcoin rose by 4.2 percent to over $35,000, a day after having slumped to nearly $30,000, having shed 46 percent of its value from its mid-April peak of $64,870.
- Additional reporting by Fin24