Top seed David Ferrer booked a place in the second round of the Copa Claro with a hard-fought 7-6(7) 6-4 opening win over Maximo Gonzalez.
Two tennis stars have now caused controversy with underarm serves at the US Open, but why are they doing it?
Order of play for day four of the US Open, with Rafa Nadal, Roger Federer, Serena Williams and Victoria Azarenka all on court.
Jerzy Janowicz was showered with boos for serving underhand during his quick opening round exit from the US Open.
* 2011 champion Stosur beaten by teenager Duval
First round: 24-Juan Ignacio Chela (Arg) beat Marinko Matosevic (Aus) 3-1 (Matosevic ret)
First round: First round: Ryan Harrison (U.S.) beat Victor Hanescu (Romania) 1-6 6-3 6-4; Andrey Golubev (Kazakhstan) beat Maximo Gonzalez (
Round-up: Juan Carlos Ferrero got the defence of his Umag title under way with victory after Maximo Gonzalez retired.
Wildcard Tobias Kamke delighted the home crowd as he eased into the second round with an emphatic 6-1 6-1 win over Pere Riba in Hamburg.
First round: Jarkko Nieminen (Finland) beat Santiago Giraldo (Colombia) 6-4 6-3;
Eighth seed Potito Starace came through his first-round clash with Julian Reister in the Swedish Open in straight sets.
First round: Pere Riba (Spain) beat Christian Lindell (Sweden) 6-4 6-2; Blaz Kavcic (Slovenia) beat Julien Benneteau (France) 6-4 4-6 7-5; M
First round: 20-Florian Mayer (Germany) beat Daniel Evans (Britain) 7-6(5) 7-6(1) 3-6 6-4
First round: Alex Bogomolov Jr. (US) beat 7-Jeremy Chardy (France) 3-6 6-4 7-6(7);
ATP World Tour Finals
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