Serena Williams' enigmatic 2014 season continues. And her comments after her latest "breakthrough" could be interpreted as her realizing she may not have too many "breakthroughs" left in her career.

Just two months after being the subject of one the most bizarre on-court displays at Wimbledon, Williams was back in the driver's seat at another Grand Slam event, the U.S. Open.

Serena Williams changes her stort about the reason behind her behavior at Wimbledon

Williams advanced to her first quarterfinals appearance at a slam this year with a 6-3, 6-3 victory over Kaia Kanepi on Monday. The top-ranked Williams is just one of two players among the field remaining seeded among the top 10. BFF Caroline Wozniacki, who is on the other side of the bracket, is the other.

She is three wins away from her 18th Grand Slam, which would tie her with Chris Evert and Martina Navratilova.

Serena Williams says she usually loses because she plays bad, not because her opponent plays well.

The New York Times characterized Williams' performance as "inconsistent, a little sloppy, and it didn't really matter."

Even coach Patrick Mouratoglou suggested that Williams has to reach another level to add this year's Open to her list of Grand Slams.

"If she wants to win here, she will have to play better," Mouratoglou said, according to USA TODAY Sports.

But Serena often is judged by a different standard than other current players on the tour because of her longtime dominance.

It's that dominance that she is either no longer taking for granted or no longer trying to live up to. And she sounded for the first time that she could be looking at the finish line of her career.

"Now I'm more relaxed," she said, according to USA TODAY Sports. "I feel like I don't have to win any more. I've had a wonderful career."

During another portion of the interview, Williams said, "Obviously, I don't want this to be the end," which could be interpreted as she didn't want her fourth-round match at the U.S. Open to be the end of her career.

Most analysts agree that Williams still is the game's best player and capable of winning multiple majors. Why would she quit when she's still on top of the tennis world?

Then again, her behavior at Wimbledon, in which she appeared disoriented and couldn't catch a bouncing tennis ball, caused such an uproar that it wouldn't be far-fetched for her to tell herself that she doesn't have to put herself through that kind of drama, that kind of scrutiny anymore.

Why should she keep playing when she tries to explain what happened at Wimbledon, and no one believes her? Why should she keep playing when she says her coach is not her boyfriend and no one believes her? Why should she keep playing when she's still accused of tanking her matches against her sister Venus or her matches to avoid playing Venus?

Serena may just be recognizing that she's in the twilight of her career and is speaking as such. But would it be that hard to believe if she walked away after the U.S. Open?

How much longer do you think Serena Williams will continue to play? Comment below or tell us @SportsWN.