NEW YORK -- Youth will be served.
Scrolling through Federer's championship matchups in Flushing Meadows of the past six years is like watching time-lapse photography. The age gap between him and his opponents widens inexorably, save for the asterisk of 2005, when a 35-year-old Andre Agassi ended a gallant run by taking Federer to four sets.
Federer and Lleyton Hewitt were both 23 when they played for the title in 2004. In 2006, a 25-year-old Federer beat Andy Roddick, a year younger to the month; 2007 and 2008 brought on first-time finalists Novak Djokovic and Andy Murray, each six years younger than Federer. Now comes the next wave.
Del Potro did not win Monday night's final because he was born in Argentina seven years and six weeks after Federer was born in Switzerland. The stat sheet would indicate that he won in part because he landed his first serves in the correct rectangle at the right time -- improving his accuracy with each set and averaging 76 percent during the fourth and fifth to Federer's 53.5 percent. He didn't bomb Federer off the court and was out-aced 13 to 8, but Federer's 11 double faults were a telling symptom of his unease as late afternoon segued to evening.
Youth served better and better as the match went along, and slugged vicious forehands, but there also was something intangible that aided del Potro. He was the guy who finally converted youth to his advantage in this tournament against a brilliantly accomplished elder. He brought strength, mobility and the very bearable lightness of being an underdog who already had declared that the day he clinched a spot in the final was the best day of his life. He was the guy who thought, Wow, I'm hanging in there with Roger Federer, and took competitive heart from that rather than figuring it was good enough for now.
"Got to give him all the credit because it's not an easy thing to do, especially coming out against someone like me with so much experience," Federer said. He added lyrically, "I think it's not easy to have a steel racket."
Like most rookie Grand Slam titlists, del Potro, who will turn 21 on Sept. 23 (he said he will spend part of his winnings on cheesecake for the occasion), didn't know what he didn't know. He didn't know what it would be like to play the quintuple defending champion and Grand Slam record holder in a tournament in which that champion had last lost 2,200 days ago. That didn't matter in the end, because del Potro also didn't know he was supposed to swoon simply because he was there.
There were moments in the match when del Potro appeared overmatched by Federer's swordplay. But every time it looked as if he'd had an arm or a leg lopped off, rather than presenting himself for more punishment like Monty Python's Black Knight, del Potro stopped the bleeding and hammered at Federer with fresh resolve.
"He just did not give up," said Martina Navratilova, who played into her late 40s and knows better than most what it's like to try to stave off youthful determination. "He could have lost the match in three sets, he could have lost it in four, he could have won it in four. But he just kept coming. Very, very strong mentally. I was very impressed."
Coming into the match, del Potro's staying power in a five-setter was a question mark. Endurance was one of the incremental factors that made the difference in the valiant match the two men played in the French Open semifinals. Instead, as was the case in the Australian Open against Rafael Nadal in January, it was Federer's level of play that dropped off in the fifth set as he sprayed 15 unforced errors around the court to del Potro's four.
Unlike the painful trophy ceremony in Melbourne, there were no tears for Federer this time, just a disorienting moment where he cradled the runner-up's hardware next to a man who towered over him. "He seemed very relaxed about [the loss]," Navratilova said. "Who knows? That's the hardest thing, to keep staying motivated."
Federer doesn't look all that much older than del Potro in the photos, just a lot shorter. Yet any champion who says he intends to play into his 30s has to be aware that at some point, youth not only serves better but generally volleys, rallies and recovers better as well. Wisdom, craft and drive will become as important as any shot for him.
"Any time Roger loses in a Slam final, it's going to attract attention -- other guys will see it as another little sign that they can do it, too," said Tennis Channel analyst Leif Shiras. There are a handful of men who might permit themselves to think that way now, and each year from now on there will be more. Tennis is fortunate that Federer can look across the net and find it in himself to want to school them a while longer.
Bonnie D. Ford covers tennis and Olympic sports for ESPN.com. She can be reached at email@example.com.