"I can play better but that's a good match for the start of a tournament," said Del Portro, who came to California from his homeland of Argentina. "I was a little tired from the trip but I'll be OK tomorrow."
With his body telling him it was well after midnight, the second-seeded Del Potro managed to put together enough winners to advance into the second round against Japan's rising star Kei Nishikori.
Del Potro, who turned pro four years ago and is ranked No. 7 in the world, is the youngest member of the top 10.
"I definitely feel the pressure," he said. "There are a lot of good players who have a step on me. I just try to play my game and get better day by day."
Del Potro's only loss among his 11 matches this season was to Roger Federer in the quarterfinals of the Australian Open.
Stoppini did not lose a set in qualifying for the main draw.
"I played a super player and he didn't play so good," Stoppini said. "I played well so it was close."
Sixth-seeded Sam Querrey rallied from an 0-4 start in the third-set tie-breaker to beat wild card Marcos Baghdatis, 6-3, 5-7, 7-6(5); and wild card John Isner, who played tennis at Georgia, beat lucky loser Ramon Delgado, 7-6 (9), 6-4, in other first-round matches. Isner recorded 22 aces in the match, including his first four points.
Stepanek had more trouble in the second set, but managed to beat Guccione for the third time in four career meetings.
Delgado replaced Guillermo Garcia-Lopez, who withdrew from the tournament because of appendicitis. According to a tournament spokesperson, Garcia-Lopez wasn't feeling very well the past few days and finally visited a doctor on Tuesday.