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.