Who can forget the 19-year-old kid from Switzerland, sinking to his knees on match point of a dramatic fourth-round, five-setter? He was in shock and awe.
The previously untouchable superstar on the other side of the net, who had won the previous four Wimbledon titles and seven of the last eight, was walking toward him to shake hands.
That was Pete Sampras, who had lost only once before that on that court since 1993.
Sampras was not only shaking a hand, but passing the torch. He kind of knew it, but was probably too proud to admit it, even to himself.
"There are a lot of younger guys coming up," Sampras said at the time, "but Roger is a bit extra special."
Sampras also said there was no need to panic, that he would keep coming back to Wimbledon. He was a month shy of his 30th birthday.
He played twice more at Wimbledon, going out early both times, and ended his career with a dramatic U.S. Open victory in 2002.
He was 31 then, pretty well cooked, and he knew it.
Federer will be 34 next month and is far from cooked. He remains an amazement to those who keep looking for a new wrinkle on his forehead, a slight limp or maybe a strand of gray hair.
Sampras was right that day back in 2001. Federer is "extra special."
Friday, he played another match to be savored. With it, he advanced to Sunday's Wimbledon final.
He beat Britain's Andy Murray, in front of a British crowd of 15,000 on Centre Court. It was a crowd that badly wanted Murray to win, but also, somehow, didn't want Federer to lose.
The score was 7-5, 7-5, 6-4 and does little justice to the drama and skill involved. Federer's play is often magnificent. Friday, it was a masterpiece. Superlatives about him are becoming cliches.
The semifinal victory put him into his 10th Wimbledon final. He has won seven, same as Sampras. One that he lost was last year, to Novak Djokovic, in a five-set thriller. Sunday, they will go at it again.
Djokovic, himself a tennis marvel and the No. 1-ranked men's player — a spot above Federer — pretty much had his way with Frenchman Richard Gasquet in the other semifinal, winning, 7-6 (2), 6-4, 6-4.
The day belonged to Federer, as it almost always does here. It takes something magical to get a British crowd on Centre Court to find affection for anybody else when one of its own is playing. They rooted Murray on. But few tears were shed when Federer won.
Murray won the toss, elected to receive, and was on his heels from that moment. Serving in a match from behind, especially when Federer is kicking up chalk on every inch of every service line and sending 20 aces your way, is not a recipe for winning.
"A lot of guys serve first, a lot of guys receive first," Murray said, rationalizing his coin-toss choice. "It really depends on your preference. The way it worked out today, I mean, the guy served unbelievable."
Federer said he understood the choice, even though he also knew how badly it backfired on Murray.
"Maybe it was a game plan to have me go first," Federer said. "It worked well for him. He created break point in his first game."
It did not work well for Murray. Once Federer saved that break point, the only one he faced in the match, Murray was always serving from a game behind. Federer's serve, on this soft summer day with wispy clouds floating overhead, was unbreakable.
Murray's wasn't bad, either. He got in 74% of his first serves. But the pressure of always needing to hold just to get even became overwhelming.
In the first set, Murray served at 5-6 and got himself in trouble at 15-40. The break points here were also set points. On the second one, Murray approached and Federer hit a backhand at his feet he couldn't dig out.
In the second set, after an incredible Murray service game at 4-5 that went for 14 minutes — a lifetime on these lightning grass courts — and featured five break points, seven deuces and five game points, Murray survived only to be back in trouble in his next service game.
In that one, Federer closed on the second break point and got a high forehand volley to finish. The way he was playing, that was as good as a match point. Murray served from behind again in the third set, faced the pressure cooker again at 4-5 and hit wide at 30-40.
"Definitely one of the best matches I've played in my career," Federer said, no small statement from somebody who has won a record 17 major titles and never lost a semifinal here.
Murray, whose one victory here against Federer was in their 2012 Olympic gold-medal match, said, "That's definitely the best he's served against me."
That might be encouraging for Djokovic fans.
Gasquet said of Djokovic: "His return is the best, because he never misses. You serve, the ball is always on your side again."
Djokovic said: "[Winning] in 2014 was even more special, because I won against the greatest player of all time on grass courts, maybe the greatest of all time overall."
Sampras, who held the record before Federer with 14 major titles and remains in any conversation about all-time greats, might vote for Federer too.
Especially if he remembers 2001 and the kid sinking to his knees and realizing he's still around, still doing it.
Roger Federer. Still defying time.