Roddick, Isner impressive in openers

American John Isner, who played the longest match ever at Wimbledon in June, defeated 21-year-old Dutchman Thiemo de Bakker 7-6(6) 7-6(8), winning the final-set tiebreaker 10-8 to gain revenge over the man who knocked him out of the grass-court Grand Slam. 

In other matches at the US Open warm-up, Spanish third seed Fernando Verdasco staved off two match points in the second set before emerging with a 4-6 7-5 7-6(6) victory over gritty left-handed German Michael Berrer. 

Fourth seed Marin Cilic of Croatia eased past Denis Istomin of Uzbekistan 6-4 6-2, while American Mardy Fish won his 11th successive tour match with a 6-4 6-3 victory over Viktor Troicki of Serbia.

Despite being a qualifier, the 23-year-old Zemlja did not back down against Roddick, relentlessly firing his crisp ground-strokes against the ninth-ranked American.

Zemlja had eight aces but was broken once in each set to suffer defeat in his first career match against Roddick.

In the third round, Roddick will face talented Frenchman Gilles Simon, who needed only 52 minutes to blitz Igor Kunitsyn 6-1 6-2.