Top-seeded Bob and Mike Bryan, who have won one match since August, lost to eighth-seeded Rohan Bopanna of India and Florin Mergea of Romania 6-4, 6-3 in a round-robin opener at the ATP World Tour Finals in London.
The Bryans fell to 1-4 against the 30-year-old, 5-foot-11 (1.80-meter) Mergea this year.
The 37-year-old Bryan twins probably must win the rest of their matches, which would give them a fifth ATP Finals title and second in a row, to keep their year-end streak alive. The former Stanford stars lead second-ranked Jean-Julien Rojer and Horia Tecau by only 65 points (6,465 to 6,400). Also in contention are Ivan Dodig and Marcelo Melo (6, 140), and Jamie Murray and John Peers (5,635).
The Bryans will play fifth-seeded Simone Bolelli and Fabio Fognini of Italy in another round-robin match on Tuesday.
Bolelli and Fognini, this year's Australian Open champions, lost to fourth-seeded Murray of Great Britain and Peers of Australia 7-6 (5), 3-6 [11-9] today.
Melo replaced the Bryans at No. 1 in the world on Nov. 2. It was the first time since Sept. 9, 2012, that neither Bryan was ranked No. 1.
The Bryans failed to win a Grand Slam men's doubles title this year for the first time since 2004. They have won a record 16 Slams in men's doubles.
ATP WORLD TOUR FINALS
Novak Djokovic (1), Serbia, def. Kei Nishikori (8), Japan, 6-1, 6-1.
Roger Federer (3), Switzerland, def. Tomas Berdych (6), Czech Republic, 6-4, 6-2.
Jamie Murray, Great Britain, and John Peers (4), Australia, def. Simone Bolelli and Fabio Fognini (5), Italy, 7-6 (5), 3-6 [11-9].
Rohan Bopanna, India, and Florin Mergea (8), Romania, def. Bob Bryan and Mike Bryan (1), United States, 6-4, 6-3.