Andre Agassi's challenge wasn't simply the 22-year-old opponent across the net.

There was the matter of mental and physical exhaustion, as well.

Having played fellow American Robby Ginepri to a draw after four sets of tennis in Saturday's U.S. Open semifinal, the 35-year-old Agassi, who had defied time and younger men to reach this improbable moment, found himself heading into his third consecutive five-set match -- a first in a career that has spanned three decades.

Agassi responded by producing his best tennis of the match -- firing more winners, fewer unforced errors and more aces -- to tame Ginepri, 6-4, 5-7, 6-3, 4-6, 6-3, and advance to Sunday's final, where world No. 1 Roger Federer awaits.

Federer, 24, the reigning Wimbledon and U.S. Open champion, earned his spot by defeating Lleyton Hewitt, 6-3, 7-6 (7-0), 4-6, 6-3, in Saturday's second semifinal at Arthur Ashe Stadium, where a star-studded crowd of 23,582 enjoyed a splendid late-summer afternoon.

"The challenge is real simple," Agassi said, with a wry smile. "Most people have weaknesses, and most people only have one good shot. I mean, Federer doesn't have weaknesses and has a few great shots. So that equates to a problem."

Agassi becomes the oldest finalist in a Grand Slam event since 1974, when 39-year-old Australian Ken Rosewall, who was among Saturday's ticket holders, played for the U.S. Open title.

While Agassi was overwhelmed by the chaos and cacophony of New York during his first U.S. Open in 1986, he has since learned to embrace its mayhem and draw strength from its boisterous fans. He has won the title twice, in 1994 and 1999. On Sunday he'll compete in the final for a sixth time, against the best of this new generation of players, Federer.

Federer holds a 7-3 record against Agassi and hasn't lost to the American since April 2002. In three meetings this year, Federer hasn't surrendered as much as a set to Agassi. Even more daunting, Federer hasn't lost a tournament final since 2003; if he defeats Agassi on Sunday, Federer will have won his 23rd final in a row.

But Agassi will have one decided advantage against the Swiss: The unabashed support of 23,000 fans, who have cheered and hooted and whistled his every stroke throughout his stirring run.

Neither Agassi nor Ginepri played his best tennis Saturday, but both gave his best effort. Each had reason to be tired: Agassi was coming off back-to-back five-set matches; Ginepri had strung together three consecutive five-setters.

The unseeded Ginepri lost his serve out of the gate, and Agassi rolled through the first set with relative ease.

Ginepri bolted to a 3-1 lead in the second set, but his body language telegraphed nothing but self-loathing as he skulked around the court, head bowed, scowling at his every errant shot. Ginepri won the set to level the match but fell apart in the third set as his serve deserted him and his attitude soured.

The momentum shifted again in the fourth set, which went Ginepri's way. But Agassi had better stuff in reserve, and he pulled them all out in the final set, getting the key break of serve to take a 4-2 lead.

It wasn't one shot or one tactic that won it for Agassi, but a full complement of drop shots, return winners, stunning "gets," crosscourt forehands and serves.

That Agassi is still competing is itself remarkable. Time and again he has confronted circumstances that would have driven many pros to retirement -- in 1997, when his ranking plummeted to 141; and as recently as three months ago, when his sciatica flared up in a first-round loss at the French Open -- only to recommit to the game, redoubling his efforts in the weight room to wring the most of his aging body. The sciatica remains, as permanent as a tattoo, says longtime trainer Gil Reyes. And Agassi manages to continue competing with the condition only with the help of periodic cortisone injections directly into the troublesome nerve in his lower back. "Nine minutes of agony," Agassi describes the procedure, in exchange for a few months' playing time.

But his longevity isn't simply a product of gym work and medical science. The balance he has found in his family, wife Steffi Graf, son Jaden Gil and daughter Jaz Elle, has been just as critical.

"I take myself a lot less seriously than before," Agassi said Saturday. "Things aren't in perspective until you see a child treat your good day or bad day with the same spirit. And I'll never have more pressure on me than I have when I clip my little girl's fingernails, you know. So for me, it's about perspective."

With his 5-set win, Andre Agassi, 35, becomes the oldest Grand Slam finalist since 1974, when Australia's Ken Rosewall, then 39, played for the U.S. title.