BRINDISI, Italy -- Top-ranked Serena Williams fought back from a set down to win her singles match over Sara Errani but couldn't produce another victory in the decisive doubles encounter as Italy beat the United States 3-2 Sunday in a Fed Cup World Group playoff.
It was Williams' first career loss in the Fed Cup, dropping to 16-1 -- 13-0 in singles and 3-1 in doubles.
Earlier, Williams put together an error-filled 4-6, 7-6 (3), 6-3 win over Errani before Pennetta routed 65th-ranked Christina McHale 6-1, 6-1.
Italy returns to the World Group and can compete for the Fed Cup trophy next year while the U.S. is relegated to World Group II.
Belarus 3, Japan 2
The result means Belarus will return to World Group II in 2016 for just the third time, while Japan will remain in Asia/Oceania Zone Group I.
The Associated Press contributed to this report.