Five minutes into trade the blue-chip Dow Jones Industrial Average was down 66.52 points (0.51%) at 13 098.67.
The broader S&P 500-stock index lost 6.98 (0.50%) to 1395.82, while the tech-rich Nasdaq fell 11.38 points (0.38%) to 3007.26.
The downturn was an ominous omen for the debut of Britain's most successful football team on the New York Stock Exchange.
The pricing for the much-awaited initial public offering was cut to $14 on Thursday from the expected $16-20 range, underscoring doubts about the team's profit-generating potential, its management, and reflecting the worries over IPOs since the flop of Facebook's May debut.
In China, meanwhile, exports and imports slowed for the second consecutive month in July, official data showed, highlighting worsening conditions in the world's second-biggest economy.
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