Delray Beach - Australia's Marinko Matosevic upset US second seed John Isner 6-4, 6-4 on Tuesday to reach the second round of the ATP Delray Beach Open.
Isner, who won all three prior meetings with the Bosnian-born Aussie last year, fired 16 aces in a losing cause, surrendering a service break in each set while squandering all three of his own chances in the 75-minute encounter.
Matosevic, ranked 78th and seeking his second ATP final after a 2012 runner-up effort here, booked a second-round date with Japanese qualifier Yoshihito Nishioka, who defeated Dutchman Igor Sijsling 7-5, 6-1.
South African top seed Kevin Anderson ousted Aussie John-Patrick Smith 6-3, 6-3 to book a second-round meeting with Taiwan's Lu Yen-Hsun, who eliminated Aussie Sam Groth 6-7 (6/8), 7-6 (7/5), 6-4.
Two other Aussies advanced, with Bernard Tomic eliminating Tunisia's Malek Jaziri 6-3, 6-3 and qualifier Thanasi Kokkinakis downing Serbia's Filip Krajinovic 6-2, 6-3.
Tomic next faces Serbian eighth seed Viktor Troicki, who outlasted France's Stephane Robert 6-7 (3/7), 7-5, 6-1, while Kokkinakis will meet Croatian fourth seed Ivo Karlovic.
US sixth seed Sam Querrey was forced to withdraw with a sore back while leading Colombia's Alejandro Gonzalez 6-3, 1-2.
"I had a sudden movement at the net and kind of jerked my back a little bit," Querrey said.
"It's an injury that I felt before, but never on a specific motion like this. My lower back just kind of tightened up and I can't really move it in any direction."
Gonzalez will next face American Donald Young, who followed up his semi-final run from last week in Memphis by defeating Croatia's Ivan Dodig 7-5, 7-5.
French fifth seed Adrian Mannarino defeated US qualifier Eric Quigley 6-4, 6-4 and faces American wildcard Denis Kudla next.Results on Tuesday from the second day of the ATP Delray Beach Open (x denotes seeding):
Steve Johnson (USA x7) bt Mikhail Kukushkin (KAZ) 6-3, 4-1, retired, illness
Bernard Tomic (AUS) bt Malek Jaziri (TUN) 6-3, 6-3
Andrey Rublev (RUS) bt Dudi Sela (ISR) 6-4, 1-6, 6-3
Viktor Troicki (SRB x8) bt Stephane Robert (FRA) 6-7 (3/7), 7-5, 6-1
Thanasi Kokkinakis (AUS) bt Filip Krajinovic (SRB) 6-2, 6-3
Alejandro Gonzalez (COL) bt Sam Querrey (USA x6) 3-6, 2-1, retired, back pain
Adrian Mannarino (FRA x5) bt Eric Quigley (USA) 6-4, 6-4
Yoshihito Nishioka (JPN) bt Igor Sijsling (NED) 7-5, 6-1
Tim Smyczek (USA) bt Stefan Kozlov (USA) 7-5, 6-2
Donald Young (USA) bt Ivan Dodig (CRO) 7-5, 7-5
Lu Yen-Hsun (TPE) bt Sam Groth (AUS) 6-7 (6/8), 7-6 (7/5), 6-4
Kevin Anderson (RSA x1) bt John-Patrick Smith (AUS) 6-3, 6-3
Marinko Matosevic (AUS) bt John Isner (USA x2) 6-4, 6-4