Brydan Klein went down 7-6 6-3 to 19-year old Mathias Bourgue at the qualifiers for the French Open in Roland Garros.
Champion Juan Monaco will face John Isner in the semis of the US Clay Court Championship, a re-match of last year's final.
Top seed Nicolas Almagro fought back to beat Frenchman Gael Monfils 2-6 6-0 6-3 at the US Men's Clay Court Championship.
John Isner prevailed in an all-American battle with Ryan Harrison to kick off his ATP Houston campaign on a winning note.
Second round: 1-Novak Djokovic (Serbia) beat Andrey Golubev (Kazakhstan) 6-3 6-2
Guillermo Garcia-Lopez booked a date with Andy Murray at the Indian Wells Masters after opening with a three-set win over Rui Machado.
First round: Santiago Giraldo (Colombia) beat Jack Sock (U.S.) 5-7 6-0 6-1
Home favourite Andy Roddick's involvement at the ATP tournament in Memphis was ended in straight sets by Xavier Malisse of Belgium.
7-Kevin Anderson (South Africa) beat Robby Ginepri (U.S.) 7-5 6-3; Juergen Melzer (Austria) beat Denis Istomin (Uzbekistan) 6-7(2) 6-3 7-6
First round: Robby Ginepri (U.S.) beat Xavier Malisse (Belgium) 6-1 6-2; Steve Darcis (Belgium) beat Steve Johnson (U.S.) 7-6(4) 7-6(5)
Rising American star Madison Keys and former top-100 player Jesse Levine clinched Australian Open wildcards after winning the US play-offs.
Second round: 18-Juan Martin Del Potro (Argentina) beat Diego Junqueira (Argentina) 6-2 6-1 7-5
Robby Ginepri (U.S.) beat Joao Souza (Brazil) 6-3 6-4 6-7(5) 6-1; 12-Gille Simon (France) beat Ricardo Mello (Brazil) 3-6 6-3 6-4 3-6 6-4
Andy Roddick lost his cool as he crashed out of the Cincinnati Open in the first round, suffering a three-set loss to Philipp Kohlschreiber.
First round: Feliciano Lopez (Spain) beat Juan Carlos Ferrero (Spain) 4-6 6-3 6-4; Alex Bogomolov Jr. (U.S.) beat Robby Ginepri (U.S.) 6-4 6
ATP World Tour Finals
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