David Marrero, left, reacts after he and Fernando Verdasco of Spain won their men's doubles final tennis match against Bob and Mike Bryan of the US at the ATP World Tour Finals at the O2 Arena in London, Nov 11, 2013. [Photo/Agencies]

David Marrero, right, and Fernando Verdasco of Spain celebrate winning their men's doubles final tennis match against Bob and Mike Bryan of the US at the ATP World Tour Finals at the O2 Arena in London, Nov 11, 2013. [Photo/Agencies]

LONDON - American duo Bob and Mike Bryan's incredible year ended in disappointment when they were beaten by Spain's Fernando Verdasco and David Marrero in the ATP Tour Finals doubles final on Monday.

Verdasco and Marrero, the sixth seeds, upset the favourites 7-5 6-7(3) 10-7 as the title went to a Spanish pair for the second successive year following the triumph of Marcel Granollers and Mark Lopez 12 months ago.

The Californian Bryan twins were looking to win their 12th title of 2013 and surpass the 11 they won in 2007 and 2010, but the world's top-ranked pair were edged out in a match tiebreak.

They did at least end the year at No 1 for a ninth time in 11 seasons having won the first three majors of 2013 before their "calendar" Grand Slam hopes ended at the US Open where they lost in the semifinals.