Then, there is the fourth semifinalist at the US Open, Sara Errani.

The 25-year-old Italian is 5 feet 4 inches, spins serves in at an average speed of 80 m.p.h. 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 US 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.

Sharapova is 12-0 this season in matches that go the distance.

In June, Sharapova completed the career Grand Slam by winning the French Open. This month, she is making her deepest run at the US 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.

Makarova, Soares win

A last-second addition to the US Open mixed doubles field, Ekaterina Makarova and Bruno Soares are now Grand Slam champions.

The unseeded duo beat Kveta Peschke and Marcin Matkowski, 6-7 (8), 6-1, 12-10 tiebreak in Thursday’s final.

Soares, a 30-year-old Brazilian doubles specialist, had turned down Makarova before the Open because he was set to play with his regular partner, Australian Jarmila Gajdosova.

But with the minutes ticking down to sign up for the tournament, he realized they didn’t have a good enough ranking to get in. If he teamed with Makarova, with whom he had played a couple of times before, they'd get in.

Soares sent his coach scrambling to try to find the Russian on the practice courts.

‘‘He went running all the way over there and talked to her and called me like 30 seconds to go and said, ‘You can sign,'’’ Soares recalled. ‘‘So very last minute, 11:59, I signed us in. I guess it work out.’’

Bryans going for fourth