NEW YORK - That Andy Roddick's last match as a twentysomething would not be his last match at the 2012 U.S. Open was hardly in doubt Tuesday, especially whenever he was launching that intimidating, tough-to-handle serve of his.

To close the first set: ace at 141 mph.

To close the second: ace at 134 mph.

To close the third: ace at 127 mph.

Yes, even as Roddick's 30th birthday approaches on Thursday, even as his body has succumbed to injury after injury, that serve is pretty much still the same as it ever was. Now that he more frequently faces opponents who grew up cheering for him - such as 21-year-old qualifier Rhyne Williams of Knoxville, Tenn., the foil for Tuesday's 6-3, 6-4, 6-4 victory - Roddick knows more than ever he needs to rely on the best thing he's got, and 20 aces helped this time.

"You really don't see that shot," Williams said glowingly about Roddick's serve.

Heading into his Grand Slam debut, the 283rd-ranked Williams had one primary concern: "I was just hoping he wasn't going to go at me with a serve."

"I'm like, 'Oh, no. Where's he going?' That's the first thing I thought of. Then it was, 'It'll be great. I can play in front of a big crowd.' It was quite an experience," said Williams, the NCAA runner-up for the University of Tennessee last year and a 12-year-old when Roddick won the U.S. Open in 2003.

That was the last Grand Slam singles title for an American man, the longest drought in history for a country that produced the likes of Pete Sampras, Andre Agassi, John McEnroe and Jimmy Connors (not to mention others such as Bill Tilden or Don Budge).

Roddick found himself in an era dominated by Roger Federer and Rafael Nadal - and, more recently and to a lesser extent, Novak Djokovic, who began defense of his U.S. Open title by overwhelming 69th-ranked Paolo Lorenzi of Italy 6-1, 6-0, 6-1 on Tuesday night - and while he is without a second major championship for his resume, he kept adapting his game to try to do just that.

Roddick dedicated himself to stronger fitness. He learned a better backhand. He improved his volleying.

"I saw the way the game was going. You have to get stronger and quicker. I don't think there was much room for a plodder who could hit the ball pretty hard," Roddick said. "It was a conscious effort, at times, and I feel like that's added to longevity a little bit."

Following Roddick into Arthur Ashe Stadium was 32-year-old Venus Williams, playing her first U.S. Open match since she pulled out before the second round in 2011 and revealed she had been diagnosed with an autoimmune disease.

"Honestly, I didn't even understand what I was going through at that time last year. I feel like just this summer I've come to acceptance. Like it takes a long time to come to acceptance, especially when you're an athlete. You see yourself as this healthy person that nothing can defeat you," Williams said. "So it takes a while before you can kind of see yourself as someone with flaws and chips in the armor. Now that I have come to accept it, it helps me a lot in how I need to prepare for my matches, the mindset I need to come into it."

After a shaky start, dropping the first two games - and even seven points in a row in one stretch - Williams used her own powerful serve to right herself and beat Bethanie Mattek-Sands of the U.S. 6-3, 6-1. One serve at 124 mph jammed Mattek-Sands' left index finger, shoving it into a racket string so hard she needed attention from a trainer.

"She was crushing her serves," Mattek-Sands said. "I don't think anyone's returning those, so I'm not going to beat myself up too much."

Venus Williams won the 2000 and 2001 U.S. Opens, two of her seven career Grand Slam titles. That's half as many as her younger sister, Serena, who began her bid for No. 15 with a 6-1, 6-1 victory over 75th-ranked CoCo Vandeweghe in Tuesday's last match in Ashe, yet another all-American affair.

"Venus is amazing. She's the ultimate role model for me," Serena Williams said. "She's the ultimate fighter and champion - everything she's gone through and is going through. I have no excuses any more. She makes me a better person."

The younger Williams won the U.S. Open in 1999, 2002 and 2008, and is among the favorites in 2012 considering the way she dominated the competition recently while winning Wimbledon and a gold medal at the London Olympics.

Three of the day's most notable upsets were turned in by young, up-and-coming Americans. In singles, 19-year-old Sloane Stephens, who is ranked 44th, eliminated 2010 French Open champion Francesca Schiavone 6-3, 6-4. And in doubles, 19-year-old Jack Sock and 22-year-old Steve Johnson knocked out the top-seeded team of Max Mirnyi of Belarus and Daniel Nestor of Canada 1-6, 7-6 (4), 6-2, while brothers Ryan and Christian Harrison defeated last year's runners-up, Mariusz Fyrstenberg and Marcin Matkowski of Poland 7-6 (3), 2-6, 7-6 (7).

One other exit of significance: 2009 runner-up Caroline Wozniacki, who began the year ranked No. 1 but has struggled and was seeded eighth, lost 6-2, 6-2 against 96th-ranked Irina-Camelia Begu of Romania. Bothered by a bad right knee, Wozniacki also lost in the first round at Wimbledon.