Roger Federer is often compared to Pete Sampras. And when Federer plays Andre Agassi, parallels are drawn between the two rivalries.
But there are differences.
Sampras and Agassi were peers with contrasting styles, battling it out. Their rivalry provided great moments in tennis. Agassi vs. Federer provides great moments in tennis with poignancy.
For while Agassi hopes to build his history with more Grand Slam titles, Federer made history last year by winning three of the major titles, leaving little left for anyone else.
Plus as Agassi points out, Federer is not Sampras.
"They're both very relaxed on the court as far as how they play the game," Agassi said last week. "They both play it very easily. But I don't feel like their weapons are the same."
Federer's weapons are formidable.
"I think he right now is playing better than anybody I've ever played, from Sampras to Agassi," said ATP tour veteran Greg Rusedski last week. " I think Pete had a better serve than Roger does, but Roger disguises it very well and builds the point. He can come forward; he can stay back.
"I think Roger, if he continues the way he's playing now, can go down as maybe the greatest player to ever play the game. That's hard to say, considering I played most of my tennis during the Sampras era."
"His biggest weapon is his forehand and his movement," Agassi said of Federer. "He's a really explosive mover. His forehand's just a nasty shot. You know, he does a lot of things really well. He does a few things really great. That makes him quite a tough player."
Tough enough that in the U.S. Open last year, Agassi was one of two men to even take a set off Federer. So far, he has not lost a set at the Australian Open.
Interestingly enough, facing such a tough opponent and taking him to five sets over the course of two days in gale-force conditions, seems to inspire Agassi.
"Roger offers me the opportunity to push myself more than I've been pushed in a long time. That's a great feeling."
Even in this Aussie Open quarterfinal (ESPN2, 3:30 a.m. ET), Federer could erase a piece of Agassi's history. If Federer wins, that will give him 26 consecutive victories, tying Agassi for the third-longest streak.
At 34, Agassi knows the opportunities are dwindling to win a major tournament.
"Yeah, well, I haven't done it at 34 yet," Agassi said after his 6-3, 2-6, 7-5, 3-6, 6-3 defeat to Federer at the U.S. Open. "And I think it gets tougher every year, from the quality of your opponents to the distractions that exist in your own life."
No. 2 Andy Roddick's not ready to throw a farewell party for his American mentor.
"He set the standard so high for himself that it's not surprising to me to see him winning matches," Roddick said after advancing into the quarterfinals on Monday. "It's not going to be surprising two years from now if he's still here winning matches.
"People have been talking about, 'It could be his last ' since before I was on tour. I've come to just really expect it."
People have come to expect Federer to win. Roger Federer has put together a 23-0 record against Top 10 players since the 2003 Masters Cup, which just happened to be the tournament where he first defeated Agassi. At the same time, Agassi is 8-5 against Top 10 players including losing his past two encounters with Federer.
So, how do you beat this guy?
"You play a perfect match, really," Agassi said.
"I mean, Roger has to show up and be at his best. And when he is, he's proven it's better than everybody else."
In addition to the majors, Federer won 11 titles last season to lead the tour.
"His backhand used to be a weakness; now it's a weapon," Rusedski said. "His return of serve, I think he's one of the best return of serve players in the world. And he can basically do everything."
"Like any great player, you can't point to a weakness, but you can point to maybe one side that's not as strong as his other side, which is not very optimistic for his opponents," Agassi said.
Either way, it should make for great tennis.
"I'm as excited as the next person," Roddick said. "I'm still a big tennis fan so I'm excited to watch it, that's for sure."
And even after winning eight major titles -- four at the Australian -- Agassi still gets butterflies.
"There's not a match I play where I'm not nervous," Agassi said. "But, yeah, I'm excited. I mean, this is what I prepare for, you know, to play the best in the biggest of situations. It's why I do this."
There haven't been many major quarterfinals where Agassi was seen as the underdog.
"I suppose it was a matter of time," Agassi said, smiling.
Federer showed a rare burst of agitation at the suggestion he might not be at a level to defeat Agassi.
"I hope so. I mean, I don't know why you ask me a question like this," Federer said. "I think I've proven myself in the past, and I know my game's good enough, you know. Also on my day where I'm not playing perfect, I know I can beat him. He's not as good as he was when he was at the top of the ranking, otherwise he would be there.
Fortunately, I'm there.
"I think he has to raise his game, not me."
"Roger's earned the respect he deserves. I want to make him go out there and prove it to me again," Agassi said.
"That's what it's about. So whatever the seedings are, whatever the expectations are, it's more important being the favorite when the tournament's over with."
Cynthia Faulkner is the tennis editor for ESPN.com.