U.S. stocks slid, following equities’ biggest gain since May, as China’s currency devaluation sparked concern across global markets that the world’s second-largest economy is headed for a deeper slowdown.

The Standard & Poor’s 500 Index declined 0.9 percent to 2,084.35 at 4 p.m. in New York, with the gauge holding above its average price during the past 200 days.

“The driving forces today continue to be macro-oriented with China the most important,” said Tom Wright, the New York-based director of equities at JMP Securities. “We spend a lot of time obsessing over Greece or Puerto Rico, but China is a much bigger economy and a much bigger problem to the global economy and devaluing the currency is shaking people up.”

China devalued the yuan by 1.9 percent, the most in two decades, after data this month showed a plunge in exports, weaker-than-estimated manufacturing and a slowdown credit growth. The surprise move rippled through global markets, sparking selloffs in emerging-market currencies, commodities, and auto and luxury stocks with exposure to China.

A rally in commodities from oil to copper helped the S&P 500 jump 1.3 percent Monday. Those trades largely reversed today on concern demand from China, the world’s biggest consumer of energy and metals, will slow and yuan weakness will erode the buying power of Chinese consumers. Similar worries about the country’s growth helped send the benchmark index down as much as 4 percent last month from its May record.

Fed Watch

The unexpected move by China’s policy makers bolstered speculation the Federal Reserve may have to delay raising rates, as the threat of a slowdown in China could harm global growth, while lower commodity prices damp inflation. The probability of a rate increase in September slipped to 46 percent from 54 percent Monday, according to futures trading data compiled by Bloomberg.

U.S. economic data today showed worker productivity struggled to gain traction in the second quarter. Less efficiency limits how quickly the economy can grow without spurring inflation, adding another variable for policy makers to consider in deciding when to raise rates. A separate report showed inventories at wholesalers jumped the most since April 2014.

Cisco Systems Inc. and News Corp. are among companies posting quarterly updates this week as earnings season nears its conclusion. Of the S&P 500 members that have already reported, 74 percent beat profit estimates and about half topped sales projections. Analysts now project a more modest drop in second-quarter earnings, calling for a 2.1 percent fall instead of a 6.4 percent decline a month earlier.