Semifinals are set for WTA Finals as Serena Williams qualifies

The WTA Championships were first sponsored by Virginia Slims, and in 1975, the tournament switched dates from October to April. Evert won her third Virginia Slims Championships title and $40,000 for defeating Martina Navratilova (pictured here).

The round robin format began (two groups of four players, after first round elimination) and Australian Evonne Goolagong won.

Australia Evonne Goolagong Cowney on the cover of SI during the Finals at LA Memorial Sports Arena.

The tournament moves to Madison Square Garden and Chris Evert takes home the title.

Evert at the Virginia Slims Championships at Madison Square Garden. Navratilova took home the title that year.

No. 1 seed Monica Seles beats Navratilova 7-5, 6-3, 6-1 to win her third year-end title.

Martina Navratilova was sad.

Steffi Graf beat Anke Huber in five-sets (yes, the final was best-of-five for a few years) to win her fourth title.

Gabriela Sabatini retired from the game at the 1996 WTA Finals.

Kimiko Date Krumm also retired at the 1996 tournament. She would return to the tour years later and still plays at 43-years-old.

Steffi Graf hung up her racket at the 1999 tournament and received...a gift.

Lindsay Davenport and Martina Hingis met in the final for the second straight year and once again Davenport prevailed.

Martina Hingis won her ninth title of the year, defeating Monica Seles in three sets.

The Finals said goodbye to Madison Square Garden after a 22-year run and relocated to Munich, Germany.

Serena Williams, making her tournament debut, wins the title after Lindsay Davenport withdraws before the final with a knee injury.

An unhappy Davenport talks to reporters after withdrawing due to a knee injury she sustained in her previous match.

Kim Clijsters stuns No. 1 Serena Williams, who had won three majors that year, to win her first WTA Finals title.

The tournament moved back to America after a one-year stint in Munich, settling in Los Angeles.

The WTA Finals has always served as a reunion of the game's legends.

Clijsters and Hingis hanging out at the beach.

Ever the stalwart, Martina Navratilova played doubles with Svetlana Kuznetsova

Kim Clijsters beat Amelie Mauresmo in the final and won $1 million, the largest prize purse ever at a women's only sporting event at the time.

The WTA Finals were sponsored by Porsche...

...That's the only reason why this photo makes sense.

17-year-old Maria Sharapova made her debut after winning Wimbledon that year.

Sharapova went on to win her only WTA Finals title, beating Serena in three sets after trailing 0-4 in the third. She has not beaten Serena since.

Amelie Mauresmo beats Mary Pierce in the first all-French final.

Justine Henin wins her first WTA Finals title and finishes the year No. 1.

In one of the most memorable finals every played at the event, Justine Henin beats Maria Sharapova 5-7, 7-5, 6-3.

The tournament moves to Doha, Qatar for three years.

The always combustible Vera Zvonareva made the final, but lost to Venus Williams 6-7 (5), 6-0, 6-2.

It was Venus Williams' first year-end title.

Serena and Venus Williams qualified for the event in both singles and doubles.

But not in ping pong.

Caroline Wozniacki came down with leg cramps.

And in the first all-Williams final of the tournament, Serena came out on top.

he event returned to Doha for the third and final time with a $4.55 million prize and No. 1 seed Caroline Wozniacki and No. 3 seed Kim Clijsters reached the final. Clijsters came out on top.

Elena Dementieva stunned everyone by announcing her retirement.

No one was prepared.

Kim Clijsters would win her last WTA Final title.

The tournament moves to Istanbul, Turkey for three years.

In her tournament debut, Petra Kvitova wins the title without dropping a set and finishes the season at No. 2.

For the first time in WTA history, eight different countries were represented at the Finals.

73,072 fans came out to Sinan Erdem Arena for the tournament, the largest attendance since 2000.

Serena Williams extended her win-streak at the event to 10 straight matches en route to the title.

The final staging in Istanbul.

Serena Williams won her fourth WTA Finals title, beating Li Na in three sets in the final.