Another surprise by Sock at U.S. Indoor

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MEMPHIS, Feb. 22 (UPI) -- Jack Sock continued his unlikely run Thursday with a straight-sets victory that put him in the quarterfinals of the U.S. National Indoor Championships.

Sock had played only one match on the ATP circuit this year prior to coming to Memphis, that outing resulting in a loss to Marinko Matosevic in San Jose, Calif.

Ranked a mere 168th in the world, the 20-year-old American stunned second-seeded Milos Raonic in the opening round of this tournament and he backed that up with a 7-5, 6-4 victory over James Blake Thursday.

Top-seeded Marin Cilic advanced past the second round by outlasting Igor Sijsling 7-6 (7-2), 3-6, 7-6 (9-7).

Cilic will next meet Kei Nishikori, who was a 6-3, 6-3 winner over Donald Young.

In other second-round matches Marinko Matosevic defeated fourth-seeded Sam Querrey 3-6, 6-4, 7-5, Alexander Dolgopolov ousted Rhyne Williams 6-4, 4-6, 6-4, Michael Russell won over Lukasz Kubot 6-2, 6-4 and Denis Istomin prevailed over Lleyton Hewitt 6-1, 6-2.