VALENCIA, Spain -- Sam Querrey beat Jo-Wilfried Tsonga 7-6 (5), 6-2 to reach the Valencia Open quarterfinals on Thursday, dealing a blow to the second-seeded Frenchman's hopes of qualifying for the ATP World Tour Finals.
The American player secured his first back-to-back ATP match wins since June. That leaves Tsonga relying on his performance at next week's Paris Masters to clinch one of the final three places for the season-ending event in London.
Tsonga would have moved up one spot to No. 6 with a win over Querrey at the City of Arts and Sciences, but his serve deserted him in the second set as the 116th-ranked American broke twice to reach the quarterfinals.
The 11th-ranked Del Potro dropped only six first service points and broke Anderson three times to ease to a victory that improved his hopes of grabbing one of those remaining London spots. The five players ahead of Del Potro dueling for those final places are all out of action.
Juan Monaco won his second-round match 6-3, 6-1 over Fabio Fognini, while 2010 finalist Marcel Granollers also reached the last eight with a 3-6, 6-3, 7-5 win over Marin Cilic of Croatia. Granollers plays third-seeded Gael Monfils next.