After dropping the first set, the native of Australia rallied to beat American Vincent Spadea, 6-7 (3-7), 7-6 (7-5), 6-4.
Eighth-seeded Andy Murray of England, playing for the first time under new coach Brad Gilbert, beat little-known Ramon Delgado of Paraguay, 6-4, 6-4. Fifth-seeded Dominik Hrbaty of Slovakia beat Gilles Muller of Luxembourg, 6-4, 4-6, 6-3.
No. 7 Dmitry Tursunov of Russia downed Edgardo Massa of Argentina, 3-6, 6-1, 3-3, when Massa retired because of cramps and nausea in the third set.
No. 16 Mardy Fish of the United States topped Tomas Zib of the Czech Republic, 6-4, 6-3.
The tournament's survivors in the nation's capital are aiming at a winner's check of $74,250.
On-court temperatures rose above 110 degrees in the afternoon matches Wednesday.