There are a lot of matchups in this tournament between guys playing at a completely different level from the last time they met. Two such men, who meet in the quarterfinals Wednesday, are No. 2 Roger Federer of Switzerland and No. 8 David Nalbandian of Argentina.
First of all, don't let Nalbandian's origins fool you. He's not a clay-court specialist. In his Wimbledon debut, he reached the final. He nearly took away Andy Roddick's first major title in the semifinals of the U.S. Open. Nalbandian's a hard-core, hard-court threat.
Then there's Federer. Compared frequently to Pete Sampras for his beautiful all-around game, Federer sliced his way through all of the top players at the Tennis Masters Cup to go undefeated last fall. It was there in Houston that Federer exacted a little revenge for five straight losses to Nalbandian with a 6-3, 6-0 victory.
However, Nalbandian is one of two men -- the other being Andre Agassi -- who has not dropped a set in this tournament yet.
Potential show stoppers
The only American woman left in the draw, Lisa Raymond faces Patty Schnyder, whom she's never beaten. But the same could be said of Venus Williams until last week. At age 30, she's hoping to be in her first major semifinal in singles. Raymond has seven major titles in doubles.
Another 30-year-old who hopes to reach his first major semifinal is Hicham Arazi of Morocco. Arazi has won only one singles title in his career, and he next faces No. 3 Juan Carlos Ferrero, who at age 23 has won 11 singles titles.
Ferrero owns a 3-2 record against Arazi. Except there's one catch: Ferrero's only beaten Arazi on clay. The two wins by Arazi came on carpet and hard court.
They did not meet at all last year when Ferrero's career hit a growth spurt. He took over the No. 1 world ranking for a brief time, won the French Open and finished runner-up at the U.S. Open.
After his fourth-round match, Ferrero said he was not able to move 100 percent because of a leg injury.
No. 2 Kim Clijsters has a 3-1 record against No. 6 Anastasia Myskina in their past four meetings. The one loss came when Clijsters withdrew because of an injury. Clijsters is once again dealing with an ankle injury, but so far it's held up well.
Both players can run into hot and cold streaks on the court, but Myskina tends to be more emotional.
Cynthia Faulkner is the tennis editor for ESPN.com.