NEW YORK - All joking aside, if this keeps up Serena Williams won't need a back-up plan.
Serena Williams returns a shot to Varvara Lepchenko during their US Open women's singles match, at the USTA Billie Jean King National Tennis Center in New York, on August 30, 2014
The 17-time Grand Slam champion, shut out in the majors this year, continues her quest for a third straight US Open title on Friday when she takes on 17th-seeded Russian Ekaterina Makarova for a place in the championship match.
On paper it's a mismatch: the two-time defending champion seeking a sixth US Open title against the left-hander from Moscow playing in her first Grand Slam semi-final.
But Williams hadn't made it past the fourth round in the first three Grand Slams of the year, a gaping hole in her resume despite five titles on the WTA tour.
"It's almost a joke for me because I have done little to no winning in the majors," she said. "I thought, take it as a joke: I better play doubles just in case I don't make it past the second round. At least I have a back-up plan.
"I think that definitely has been able to help me to relax."
A relaxed and ever-more confident Williams is the only top-eight seed still standing in a women's draw rocked by upsets.
In Friday's other semi-final, 10th-seeded Caroline Wozniacki, a former world number one and the 2009 runner-up, takes on China's Peng Shuai, who has finally made it past the fourth round of a Grand Slam in her 37th attempt.
Williams arrives in the last four off a storming quarter-final win over tough Italian veteran Flavia Pennetta.
She erased a quick 0-3 deficit by winning six straight games as she stretched her record against the Italian to 6-0 with a 6-3, 6-2 triumph.
But she has a healthy respect for Makarova, who beat her in the fourth round at the 2012 Australian Open.
"Makarova moves well," Williams said. "She doesn't care who she plays, she gives 100 percent.
"She has that serve that can go out wide or you never know where it's going to go. She has a great backhand and she's improved her forehand."
Makarova said the key to capitalizing on those attributes would be to stay aggressive.
"Because she's so aggressive, yes? And I need to be a little bit more aggressive than she is, let her move, definitely."
Makarova's run to the semis included a fourth-round upset of seventh-seeded poster girl Eugenie Bouchard.
In the other half of he draw, Wozniacki sent French Open champion Maria Sharapova packing in the fourth round while Peng ousted fourth-seeded Agnieszka Radwanska.
- Wozniacki on the rise -
Wozniacki will be playing in her first Grand Slam semi-final in three years.
The knock on the Dane when she was atop the rankings back in 2010 and 2011 was that she hadn't won a Grand Slam title.
She came closest with a runner-up finish at the US Open in 2009, when she was 19.
She also reached the semi-finals in 2011, but she fell out of the top 10 in the world rankings this year amid a spate of indifferent results.
That included a first-round exit at the French Open, shortly after a very public breakup with golf star fiance Rory McIlroy.
Since then, a re-focused Wozniacki has won her first title of the year, and 22nd of her career, at Istanbul in July.
"I feel confident and I feel comfortable out there," Wozniacki said. "I have been playing well in these last few months. It's just nice that it's paying off here.
"I'm just happy I'm on my way up again."
Wozniacki has beaten the 39th-ranked Peng in five of six career meetings, Peng's only victory in the series coming back in 2007.
The Chinese veteran -- better known for her doubles prowess, reached a career-high 14th in the rankings in 2011, but the erratic progress of her singles career had her contemplating giving up the sport in 2006.
But she hung on -- just as she had as a 12-year-old when the discovery of a heart defect almost stopped her career before it began.
Despite her dominance of Peng, Wozniacki said she was expecting a challenge from the 28-year-old, who joined two-time Grand Slam champion Li Na and Zheng Jie as the only Chinese players to reach a major semi-final.
"She's playing aggressively," Wozniacki said. "She she's strong from both sides. She's been serving well. It's going to be a difficult match."