Serena continues to play through the pressures that come with Slam bid

Tsvetana Pironkova has played the Cincinnati WTA Premier event five times; this year was the first time the current No. 42-ranked player won a match.

Serena Williams has played the tournament six times. She's the defending champion, and also reached the 2014 final. She is the best player in the world and winner of 68 singles titles to Pironkova's one.

So how is it that Pironkova had three break points compared to just two by Williams in their second-round match at the Western & Southern Open on Wednesday and gave Williams all she could handle over the course of two tough sets?

The best answer is, strange things happen to a marked man or woman. That's just what Williams is these days, as she prepares to make a final push to become the first woman to complete a calendar-year Grand Slam since Steffi Graf in 1988. It means living with a target on your back, and that's an uncomfortable feeling.

Not that Williams isn't accustomed to it; but, this time, it's a little bit different. Williams, who has accomplished just about everything in tennis a few times over (for starters, she has 21 Grand Slam singles titles) has never won all four majors in a single year -- something that only two other women in the Open era have accomplished (Graf and Margaret Court in 1970).

On the brink of making history, Serena seems jittery about it. She has had to wonder how to handle the period between Wimbledon and the US Open, in terms of how completely to expose herself to the pressures that will only mount until the calendar Slam chase is resolved one way or the other.

In her first scheduled tournament after Wimbledon, Williams played one match in Bastad, Sweden, before pulling out after the victory to protect her sore elbow. She later withdrew from the Bank of the West Classic in Stanford for the same reason. Williams returned to action at the Rogers Cup and lost in three sets against Belinda Bencic in the semifinals.

Williams' performance against Pironkova was an improvement from her loss to Bencic, but it's clear that she's still pressing. Her serve comes and goes like the sun on a cloudy day. She broods; she appears careworn; her outbursts when she makes good shots at a key moments seem excessive, as if she has forgotten that she is, after all, Serena. Those miraculous shots are what she does, are who she is. In her post-match interviews, she repeatedly uses the words "stress" and "intensity" and "focus" when describing her form.

Granted, Pironkova had a good day by any standard. She made just 14 unforced errors (compared to 36 by Williams) and won an impressive 56 percent of the second-serve points she hit (compared to 42 percent by Williams). Coincidence? Probably not.

This is the kind of situation and the kind of player Williams will face until her US Open run ends. Every opponent will have an extra spark of motivation when she faces Williams, while Williams herself grapples with pressure and how it works on her mind and game. The closer Williams gets to her goal, the more enthusiastically her rivals will want a shot at her.

What do they have to lose? If you can't be the player trying to accomplish a historic feat, you may as well be the one to stop it. And stopping it entails a whole lot less work.