Tennis champion Serena Williams put the discussion of whether she's one of the best women's players to bed long before her dominating run this year. In fact, the only argument left about the younger Williams sister is where she ranks on the list among the greats. She is already one of the top five or six women's tennis players of all time, and she continues to make her case for the top three.

When she is finally finished with her career, it will, without question, be considered among the best, along with those of athletes such as Steffi Graf, Chris Evert, Martina Navratilova, Margaret Court and Helen Wills Moody.

Williams started gaining national attention before the turn of the new millennium when she won her first grand slam at the 1999 U.S. Open. She is still winning grand slams 16 years later in a career that has had more ups than downs.

Since her first grand-slam victory, there have only been five years (2000, 2001, 2004, 2006 and 2011) in which Williams didn't win a grand slam in any of the four events. Of those five years, she failed to reach at least one grand-slam final twice (2000 and 2006).

She has proven herself on all types of tennis-court surfaces. She has won on hard court, clay court and on grass. The French Open clay courts have yielded her the least amount of grand slam wins with just three. She has also taken the U.S. Open, Australian Open and Wimbledon six times each.

Since the open era, which began in 1968, when professionals were allowed to play in the majors along with amateurs, only Graf won more majors than Williams with 22 victories in her stellar career. Williams has 21 majors behind her name and could tie Graf with a win in the 2015 U.S. Open.

Williams already has a career grand slam from winning the Australian Open, French Open, Wimbledon and the U.S. Open, which she achieved in 2003, a feat that only 10 women have accomplished. Williams has also completed the career grand slam in women's doubles tennis with her sister, Venus.

She completed the "Serena Slam," having all four grand-slam titles at once but not in the same year, in 2002 and 2003, beginning with the 2002 French Open and finishing with the 2003 Australian Open. Williams has achieved this twice now, completing her second "Serena Slam" by winning this year's Wimbledon and the 2014 U.S. Open.

Williams also completed the "Career Golden Slam" by winning all four majors and an Olympic gold medal in 2012. This was the second time she won the "Career Golden Slam," having also completed the feat with her sister in mixed doubles.

Williams has also earned the "Career Super Slam," which is winning all four grand slams and the year-end Women's Tennis Association Tour Championship. This leaves Williams very little left to accomplish in her career, but there are a few markers she could reach yet, starting with the 2015 U.S. Open.

She is currently just two wins away from winning, and with those, she will accomplish two more feats to strengthen her place in the top of women's tennis history.

If Williams wins the 2015 U.S. Open, she will finally have the "Calendar Grand Slam," winning all four grand slams in the same year. Graf was the last women's tennis player to accomplish the calendar slam in 1988, a year in which she also won the gold medal in the Olympics for the only "Golden Slam." Only three women—Graf, Court and Maureen Connolly Brinker—have managed the "Calendar Grand Slam" thus far.

Also, a win at the 2015 US Open would make 22 grand slams for Williams, tying her with Graf for most grand-slam wins in the open era, and it will leave her two grand slams wins behind Court.

Williams will turn 34 later this month, and while that isn't normally considered old, in the world of sports, it is near the end of the line for even the best players. But if Williams can complete her sweep of the 2015 grand slams, one has to wonder when the great will slow down or slip from the top of the sport.

Williams hits the court tonight, Thursday, Sept. 10, from 6 to 10 p.m., to face Italian Roberta Vinci. If Williams reaches the finale, it will be on Saturday, Sept. 12, from 2 to 5 p.m. ESPN will televise both matches.