A rare doubles pairing of Serena Williams and Venus Williams saw the sisters lose 7-6 (5), 6-4 to the Czech duo of Linda Noskova and Lucie Hradecka in first-round action at the U.S. Open in New York on Thursday.
The match is expected to be the final doubles match that the sisters play together.
Noskova and Hradecka saved four of the five break points they faced and finished with a 44-29 advantage in winners.
Hradecka is ranked No. 25 in the world in the world in doubles while Noskova is ranked No. 209. Serena Williams is rated 413th in doubles while Venus Williams has no ranking due to a lack of matches.
The Williams sisters have won 14 Grand Slam doubles titles together without ever losing a championship match. They won the U.S. Open doubles crown in 1999 and 2009.
Serena Williams, 40, has indicated that retirement is in her near future, making this Open a likely farewell tour. The 23-time Grand Slam singles champion has won two singles matches in this tournament, most recently upsetting second-seeded Anett Kontaveit of Estonia 7-6 (4), 2-6, 6-2.
"It's no rush here, I'm loving this crowd, and it's really fantastic," Williams said after the Wednesday singles win. "There's still a little left in me. We'll see."
All eyes will now be on Serena Williams' third-round match against 46th-ranked Ajla Tomljanovic of Australia on Friday, which could either continue a magical run or potentially end her impressive career.
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