Three Others Left Standing Face One Very Tall Challenge

So who can still stop the first Grand Slam in 27 years?

Only three candidates remain at the U.S. Open, four if you count Serena Williams, who has been known - though not lately - to be her own biggest tennis enemy.

But Williams, who is now just two victories away from a Grand Slam, has shown nothing but resilience under mounting pressure throughout this tour de force of a season.

Odds are, it will require something resembling the match of a lifetime to take her out at this late stage of the game. And the only women who still have a chance to produce that match are Roberta Vinci, Williams' unseeded semifinal opponent, and Simona Halep and Flavia Pennetta, who will meet in the other semifinal on Thursday night (New York City weather permitting).

Halep, the No. 2 seed, is naturally the biggest threat, and she underscored it on Wednesday afternoon with a resilient, deeply entertaining 6-3, 4-6, 6-4 victory over Victoria Azarenka, the talented and combative Belarussian who was many pundits' top pick for a Grand Slam spoiler.

Azarenka was also the only other woman left in the draw beside Williams who had won a Grand Slam singles title, and also the only one to have pushed her hard at both the French Open and Wimbledon this year. Without her, Williams is even more in a statistical class of her own.

She has 21 major singles titles and a total of 69 career titles. Halep, Pennetta and Vinci have 30 career titles among them and only one Grand Slam singles final, which Halep lost to Maria Sharapova at the 2014 French Open.

Williams has career prize money of more than $73 million; Halep, Pennetta and Vinci have a collective $28 million. (Can Serena Crask the Vinci Code?)

In head-to-head terms, Williams is 4-0 against Vinci, 7-0 against Pennetta and 6-1 against Halep, although that lone loss was a memorable one, with Halep defeating Williams, 6-0, 6-2, in the round-robin phase of last year's WTA Championships in Singapore.

Williams quickly avenged that stunning rout by dismissing Halep, 6-3, 6-0, in the final of that tournament. Their two matches since then have been much less lopsided, including a gem of a three-setter won by Williams in the semifinals of the Miami Open and a 6-3, 7-6 (5) victory by Williams in the Cincinnati final last month.

"I still think Azarenka would have been a bigger threat," Chris Evert, the former champion who is now an ESPN analyst, said in an interview on Wednesday. "Halep will have to serve like today with more pace. She's been pushing her serve the whole tournament and looking negative. Today, however, was a lot more positive. Her backhand is lethal. But I think Halep can give Serena trouble if she believes."

Belief should not be enough for Vinci, even if the crafty Italian has the ability to play tricks with Williams' timing by slicing and varying pace. But for all those who might see a Williams-Halep rematch in the Open final as a foregone conclusion, it is best to remember that Pennetta has a 3-1 career edge over Halep even if Halep has won their only match in the last two years - 6-3, 7-5 in the round of 16 in Miami this year.

"To make a winner to her you have to finish the point seven times," Pennetta said of Halep after defeating Petra Kvitova in another three-set quarterfinal tussle on Wednesday. "The ball is always coming back. It's going to be like a marathon, I think."

Whatever happens, it has been 27 years since tennis had a homestretch like this.

Since Steffi Graf's Grand Slam in 1988, no other player - man or woman - has come this close to winning all four of the major singles titles in the same calendar year.

The majority opinion among those who have seen both Graf's and Williams' runs from close range is that Williams is dealing with more pressure.

"Much more pressure on Serena," Evert said. "Social media. The drama in her comebacks. Being American. Her story and journey transcend the sport. Steffi was quiet, sheltered, and Grand Slams were not as big as they are today. Steffi might have had German press following her every move. Serena has worldwide press."

In 1988, Graf did not even have to play her semifinal. Evert, in the final stages of her career, had to withdraw after becoming ill with a stomach virus.

"I was vomiting in my room all night and morning," Evert said. "The tournament doctor came to visit me in my hotel room. I can't remember any other time I defaulted."

But Graf certainly had to fight to tick the final box of her Grand Slam, requiring three sets to beat Gabriela Sabatini in the final, 6-3, 3-6, 6-1. Although it was Graf's first U.S. Open title, her prevailing sentiment was much closer to relief than pure joy.

"I sensed so much expectation all around me that was not my expectation," Graf said in an interview with the French sports newspaper L'Equipe this year. "It became suffocating and it quite frankly kept me from concentrating on my tournament."

© 2015 New York Times News Service