The five-time US Open winner beat Melzer, 6-3, 7-6 (4), 6-3 yesterday, for yet another straight-set victory at Flushing Meadows. Next up - a meeting with one of the few players who has enjoyed success against both Federer and Rafael Nadal on the sport's biggest stages.
That would be No 5 Robin Soderling, who defeated No 21 Albert Montanes 4-6, 6-3, 6-2, 6-3 to reach the US Open quarterfinals for the second straight year.
The runs at the US Open are nice, but where Soderling has really made his name is against Nadal and Federer at recent French Opens.
He beat Federer at this year's French Open to end Fed's string of 23 straight Grand Slam semifinal appearances. Last year, Soderling notched a fourth-round victory over Nadal at Roland Garros that, coincidentally, simplified Federer's path to finally complete the career Grand Slam. With Nadal out of the way, Federer's opponent in last year's French final: Soderling.
The Swede, ranked a career-high fifth at this year's US Open, is one of only two players (Juan Martin del Potro is the other) with Grand Slam victories over both of the world's top two players.
"I think it's always a very nice feeling to play against the world's best," Soderling said. "It's matches like that that you train for. It's matches like that I've been dreaming of playing since I started playing tennis. You know, playing at the big courts in the big tournaments. It's very fun."
So far, Federer has been enjoying his stay at Flushing Meadows, where he has won 44 of his last 45 matches - the only loss coming to del Potro in last year's final. The second set of the Melzer match offered some perspective into how difficult it can be to break through against the player with a record 16 major titles.
After exchanging early breaks, the players held serve to play it out to a tiebreaker.
It was there that Federer, who doesn't need any extra help, twice hit balls that dribbled off the net cord and over for winners. He also won a point after a replay that came when a bad line call nullified Melzer's solid return of Federer's serve. It added up to a 7-4 win in the breaker, and when he lost set point, Melzer looked skyward and screamed in frustration.
"I wasn't happy with my fortune. Let's put it that way," Melzer said.
When they shook hands at the end, Federer apologized to him about the second-set tiebreaker.
"I think I deserved the second set," Melzer said. "You couldn't be more lucky in a tiebreaker than he was in this tiebreaker."
Federer admits he is taking nothing for granted against Soderling, whose victory at the French this year was the first in 13 meetings between the players. The match came after a rainstorm, when the red clay at Roland Garros was moist and slow. Still, Federer knows, a win is a win.
"I expect it to be really tough, especially now that he's gotten a taste of how to beat me," Federer said. "It's up to me to clean up my game and put in a good performance."
In the quarterfinal opposite Federer-Soderling, No 3 Novak Djokovic will play No 17 Gael Monfils. Djokovic dispatched No 19 Mardy Fish 6-3, 6-4, 6-1 to leave only one American man in the draw, No 20 Sam Querrey.
Querrey plays No 25 Stanislas Wawrinka today in a quarter of the draw that doesn't have a top-10 seed left.
"I think the world of Sam's game," Fish said. "I really think he's got a lot of upside. If he were a stock, I'd buy big time."
In the featured women's match yesterday, No 1 Caroline Wozniacki defeated No 14 Maria Sharapova 6-3, 6-4 in a match that saw Sharapova commit 36 unforced errors to only 10 from Wozniacki.
In other words, Sharapova did what everyone does when they play "Woz" - the human backboard.
Not that there's anything wrong with that, said Wozniacki.
"I think that's great tennis when there are good rallies," she said. "I think it's good for the crowd, as well. It just feels great, when you feel like you're hitting the ball right, it's in the middle of your racket, the ball does whatever you want it to do."
Which has pretty much been the case for Wozniacki, who is trying for a return trip to the finals at Flushing Meadows. Counting the Sharapova match, she has lost a grand total of 10 games in four matches and she has committed only 40 unforced errors, compared to 123 by her opponents.
"She's retrieving a lot of balls. She served really well today. She used the wind really effectively," Sharapova said. "She was able to use many things to her advantage."
Next, Wozniacki plays unseeded Dominika Cibulkova, who defeated No 11 Svetlana Kuznetsova 7-5, 7-6 (4) yesterday. The bottom half of that side of the bracket pits No 31 Kaia Kanepi vs No 7 Vera Zvonareva.
The other side of the women's draw is tougher. In quarterfinals today, it will be No 2 Kim Clijsters, the defending champion, against No 5 Sam Stosur, and No 3 Venus Williams against No 6 Francesca Schiavone.
The men's fourth-round matches feature an all-Spanish quadrant: No 1 Rafael Nadal vs No 23 Feliciano Lopez and No 10 David Ferrer vs No 8 Fernando Verdasco.