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Washington, DC (Sports Network) - Top seed and two-time champion Juan Martin del Potro won a pair of matches Thursday to reach the quarterfinals at the $1.3 million Citi Open tennis event.

The second round had to be completed on Thursday after rain from Wednesday caused a backup in the schedule. Del Potro, who titled here in 2008 and 2009, handled American Ryan Harrison 6-1, 7-5 in a second-round encounter before earning a 6-3, 6-3 victory over No. 14 seed Australian Bernard Tomic.

The quarterfinal opponent for the native of Argentina will be South African Kevin Anderson. The No. 7 seed also won twice Thursday, first beating Aussie wild card James Duckworth, 6-3, 3-6, 6-4; and then topping American Mardy Fish, 7-6 (7-2), 6-1 on the hardcourts at FitzGerald Tennis Center. Fish was denied his 300th career win.

No. 2 seed Kei Nishikori of Japan beat American wild card Jack Sock in the second round, but then was ousted from the tournament later in the day by No. 16 seed and 2010 runner-up Marcos Baghdatis, 6-1, 6-2.

Towering American John Isner, the No. 8 seed and 2007 runner-up, will face Baghdatis in the quarterfinals. Isner upended India's Somdev Devvarman, 7-5, 7-5, in round three.

Third-seeded German Tommy Haas, last year's DC runner-up to Alexandr Dolgopolv, also won twice on Thursday. He overcame American qualifier Tim Smyczek 3-6, 7-5, 6-3 in round two and then toppled No. 13 seed Ivan Dodig of Croatia, 6-4, 4-6, 7-5.

Aussie Marinko Matosevic toppled fourth-seeded Canadian Milos Raonic, 7-5, 7-6 (9-7) in the third round. His next opponent will be Russian Dmitry Tursunov, who ousted Czech Radek Stepanek, 4-6, 6-4, 7-5. Stepanek titled here two years ago.

Bulgaria's Grigor Dimitrov, the 11th seed, eliminated American Sam Querrey, the No. 6 seed, 6-3, 6-2 in third-round play. Dimitrov will play Haas in the quarterfinals.

The 2013 Citi Open champ will collect $292,200.

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