Then, there is the fourth semifinalist at the U.S. Open, Sara Errani.
The 25-year-old Italian is 5-foot-4, spins serves in at an average speed of around 80 mph and yet, somehow, keeps getting her name in the conversation at the biggest events in tennis.
A runner-up at the French Open, 10th-seeded Errani has vaulted 35 spots in the rankings this year, debunking the thought that only power players with power games can succeed at the highest level.
"It's the best year of my life, of course," Errani said.
She can make it even better with a victory in Friday's semifinal against fourth-seeded Williams, who is having a pretty strong season herself. The winner at Wimbledon and the Olympics, Williams has steamrolled through her first five matches at the U.S. Open, losing a total of 16 games.
More daunting than that: She insists she hasn't even started playing "Serena Tennis" yet.
"I feel like I'm going to get more focused and serious and start playing `Serena tennis' in the next couple of rounds, if I get to play two rounds," she said. "That's my goal."
The other semifinal pits No. 3 Sharapova against top-seeded Azarenka in a rematch of the Australian Open final, where Azarenka won a tight first set, then closed out the second in 36 minutes for a 6-3, 6-0 victory.
They have met twice since, splitting the matches, with Azarenka winning the hard-court matchup at Indian Wells in March and Sharapova winning on clay in Stuttgart in April.
"Maria is always one of these players that will give it all, no matter what the score is," Azarenka said. "She's always fighting and she's really tough mentally."
If there was any doubt about that, Sharapova has erased it on her road to the semifinals this year. She was cruising in her fourth-round match when she topped Nadia Petrova 6-1 in the first set. But Petrova gathered all the momentum and won the second. Sharapova was trailing 2-0 in the third set when a rainstorm stopped play.
After receiving a pep talk from her dad, Sharapova came back out, captured five of the next six games and won the match.
Rain helped her in her next match, as well, halting play when she was trailing 4-0 to Marion Bartoli. The next day, Sharapova returned to the court for another three-set victory. Bottom line, Sharapova is 12-0 this season in matches that go the distance.
"It's a great statistic," Sharapova said. "It shows that I enjoy the battle no matter what the score is."
In June, Sharapova completed the career Grand Slam by winning the French Open. This month, she is making her deepest run at the U.S. Open since winning it in 2006.
If she wins, she'll get a rematch, either with Errani, whom she defeated 6-3, 6-2 in the final at Roland Garros, or with Williams, whose last match against Sharapova was a 6-0, 6-1 whitewashing in the Olympic final.
Williams insists she hasn't returned to that level since then, even though the statistics say differently. During one period that spanned three matches, she won 23 straight games.
"I don't keep up with those stats," Williams said.
Though the margins of her matches and the way she's playing would seem to make her a favorite, Williams isn't getting wrapped up in how the match looks on paper. But if she did, she'd find she's more than four inches taller, her serve is more than 30 mph faster and she has 14 more Grand Slam titles than Errani. She leads the series with Errani 3-0 but they haven't met since 2009. Venus Williams has defeated Errani three times since then -- including twice this summer -- and Serena says she'll certainly go to her sister for a scouting report.
"I can't underestimate her," Williams said. "It's not by luck she's been doing so well."
In her previous two appearances here, 2009 and 2011, Williams looked like the strongest player left come the semifinals. Both times, she had confrontations with officials calling the match. Williams delivered her infamous foot-fault tirade and was docked match point in the 2009 semifinals against Kim Clijsters, then went into a "You're just unattractive inside" monologue directed at the chair umpire after a hindrance call in the 2011 final against Sam Stosur.
Stosur, who fell in a third-set tiebreaker to Azarenka in the quarterfinals, gave credit to the top-ranked Belarusian but said it's hard to pick against Williams.
"If anybody's going to beat her they have to play very well, be aggressive, hit winners, not give her anything, and try and temper her serve," Stosur said, recalling the formula that helped her win her first Grand Slam title last year. "Serena, when she's on, is pretty tough to beat."