NEW YORK -- His ranking down, his health a question mark much of the season, Andy Roddick figures nothing will come easily at the U.S. Open.
Roddick held on to avoid a first-round upset Wednesday night at the Grand Slam tournament he won in 2003, beating 96th-ranked Michael Russell 6-2, 6-4, 4-6, 7-5.
"Wasn't pretty," the 21st-seeded Roddick said. "I'm certainly not fooling myself by thinking that was worthy of a championship performance, by any means. But, you know, I don't know if I would expect that."
Not all that long ago, Roddick wasn't even sure whether he'd be able to enter the U.S. Open because of a torn abdominal muscle. He was helped by a 13-0 edge in aces in the all-American matchup against Russell.
"I'm trying to get my form there, I promise you," Roddick said. "You know, a lot of people, when they're coming back, do it on the side courts. I just have an audience."
After breezing through the first two sets against Russell, Roddick began to run into trouble in the third and then fell behind by a break in the fourth.
"I had the momentum. I felt Andy was getting a little bit frustrated. He was missing a lot of returns. I mean, the crowd was starting to get into it," Russell said.
"I felt he would kind of maybe panic a little bit if we went to a fifth," said Russell, who fell to 0-7 at the U.S. Open and 6-23 at all Grand Slam tournaments.
Roddick -- whom Russell called "kind of the poster boy for American tennis the last 10 years" -- broke right back to even the fourth set at 3-all. Then, trailing 6-5, Russell double-faulted to give Roddick a match point before netting a volley to end it.
Struggling with various injuries, former No. 1 Roddick is having a tough season, and his ranking dropped outside the top 20 for the first time in a decade.
Roddick, who turned 29 on Tuesday, will face 18-year-old Jack Sock of the United States next. Both were born in Nebraska.
"I was joking with someone today," Roddick said. "I said, 'I think we're the only two teenagers to play tennis in Nebraska in the last 30 years, and we're both in the U.S. Open.'"
Sock earned his first Grand Slam victory, beating the oldest player in the draw.
The 18-year-old defeated Marc Gicquel of France 6-4, 6-3, 1-6, 6-4. At 34, the 96th-ranked Gicquel is 15½ years older.
Sock lost in his Grand Slam debut at Flushing Meadows last year in four sets.
He earned a wild card both years by winning the U.S. Tennis Association's boys under-18 national championship. He captured the U.S. Open junior title in 2010, the first American to win the boys championship since Roddick in 2000.
The match between two big servers featured 25 aces, 14 for Isner. The 28th-seeded Isner topped out at 141 mph and Baghdatis, the 2006 Australian Open runner-up, at 132 mph.
Isner's next match is against another American, Robby Ginepri, who also won Wednesday.
Andy Murray needed 1 hour, 10 minutes to win his first set and then only seven minutes more than that to win the next two in advancing to the second round with a 7-6 (5), 6-2, 6-3 victory over Somdev Devvarman.
Murray, in search of his first Grand Slam title, was leading world No. 1 Novak Djokovic in the final at Cincinnati earlier this month when Djokovic retired with a shoulder injury for only his second loss of the year.
Murray fell down a break early in Wednesday's first set but battled back to force a tiebreak. After winning that, he slowly wore down his opponent, a 26-year-old from India who has never been past the second round in a Grand Slam.
Juan Martin del Potro played at the U.S. Open for the first time since winning in 2009, beating Filippo Volandri of Italy 6-3, 6-1, 6-1. The 18th-seeded Argentine was unable to defend his title last year because of a wrist injury.
Benneteau, who got a wild card into the main draw, saved 12 of 13 break points and snapped a seven-match losing streak against opponents ranked in the top 10.
The Frenchman lost in the first round in five of his previous seven U.S. Open appearances. Now he'll try to reach the third round for the second time, matching his 2009 showing.
Almagro had dropped his opening match at Flushing Meadows only once before, in 2006.
In other results, 12th-seeded Frenchman Gilles Simon held off Ricardo Mello of Brazil 3-6, 6-3, 6-4, 3-6, 6-4; No. 25 Feliciano Lopez of Spain beat Tatsuma Ito of Japan 6-2, 6-4, 6-4; Denis Istomin of Uzbekistan rallied past American Ryan Sweeting 3-6, 7-5, 6-4, 7-6 (4); and, in an all-American match, Alex Bogomolov Jr. rallied past Steve Johnson 4-6, 4-6, 6-3, 7-6 (3), 6-3.
Information from The Associated Press was used in this report.