''I'm fairly relaxed, and I was feeling the ball well this morning,'' Pospisil said. ''When I'm feeling the ball well, I don't panic.''
In other second-round matches, Slovakia's Lukas Lacko beat sixth-seeded Denis Istomin of Uzbekistan 5-7, 6-1, 6-4; Israel's Dudi Sela topped ninth-seeded Sam Querrey of the United States 6-2, 6-4; and American Jack Sock beat New Zealand's Michael Venus 6-4, 6-2. Seventh-seeded Yen-hsun Lu of Taiwan beat American Alex Kuznetsov 6-4, 6-4 in a first-round match.
''Sam didn't serve his best that game, and I took that to my advantage,'' Sela said. ''I think I'm moving fairly good, better than before.''
Defending champion John Isner, the No. 1 seed, will open play Thursday against wild-card entry Robby Ginepri of Atlanta. Ginepri beat Ukraine's Sergiy Stakhovsky on Tuesday.
South Africa's Kevin Anderson, the No. 2 seed who lost to Isner in the final last year, will start play Thursday against qualifier Thiemo de Bakker of the Netherlands.