Flushing Meadows, NY (My Sportsbook) - Battling a sore back, fifth-seeded Englishman Tim Henman needed all five sets Tuesday to sneak past big Croat Ivo Karlovic in the opening round of the U.S. Open. Meanwhile, former champion Marat Safin of Russia was a disappointing first-round loser on Day 2 at the year's final Grand Slam event.

Henman, who injured his back while practicing over the weekend, edged out the 6-foot-10 Karlovic 7-6 (7-3), 6-7 (7-9), 4-6, 6-4, 6-4 at Armstrong Stadium on the grounds of the USTA National Tennis Center. The Brit advanced with the help of three breaks, as Karlovic possesses one of the biggest service games on the men's tour.

Karlovic launched 39 aces at Henman, but the big Croat also piled up 13 double faults and 54 unforced errors, as Henman prevailed despite striking 53 fewer winners (123-70) than his tall counterpart.

Up next for the French Open semifinalist Henman will be Frenchman Jerome Golmard.

The 13th-seeded Safin appeared listless in a 7-6 (7-5), 6-4, 3-6, 6-3 defeat at the hands of former top-10 player Thomas Enqvist of Sweden. Safin captured the 2000 U.S. Open by whipping the legendary Pete Sampras in the final here and is a two-time Australian Open runner-up, including earlier this year against Swiss star Roger Federer.

Tenth-seeded Olympic gold medalist Nicolas Massu of Chile reached the second round by pasting Argentine Jose Acasuso 6-4, 6-0, 6-2. The gritty Massu captured both men's singles and doubles gold in Athens less than two weeks ago.