Semifinals are set for WTA Finals as Serena Williams qualifies

SINGAPORE -- Serena Williams' fate at the WTA Finals was out of her hands on Friday, but thanks to Simona Halep -- the woman who gave her one of the worst losses of her career on Wednesday -- Serena has qualified out of the group stage and into the knockout round at the WTA Finals.
Serena clinches No. 1 and Wozniacki, Radwanska in semis
Serena finished 2-1 in the Red Group and was into the semifinals as long as Ana Ivanovic did not beat Halep in straight sets on Friday. Serena's camp was left sweating after Halep served for the first set at 5-4, only to get broken and then lose a dramatic tiebreaker 9-7. With Ivanovic one set away from knocking Serena out of the tournament, Serena's hitting partner, Sascha Bajin, felt the stress:
Aaaahhhhhhhhhh!!!!!
— sascha Bajin (@BigSascha) October 24, 2014
But Ivanovic couldn't sustain her momentum. Her first set comeback left her physically taxed and Halep was able to win the second set 6-3 to eliminate Ivanovic from the tournament. With that, Halep qualified in the first position out of the Red Group and Serena qualified second.
And off to book a practice court for tomorrow I go... 😁😁😁😁
— sascha Bajin (@BigSascha) October 24, 2014
Ivanovic came back in the third set on Friday to beat Halep 7-6(7), 3-6, 6-3 and finish off a great season, where she won four WTA titles and made a long-awaited return to the top ten. Saturday's semifinals will see a U.S. Open final rematch when Serena takes on Caroline Wozniacki. Serena leads the head-to-head 9-1. Halep will play AgnieszkaRadwanska in the other semifinal. Radwanska leads that head-to-head 4-2.
GALLERY: HISTORY OF THE WTA FINALS
The History of the WTA Tour championships
1975
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).
1976
The round robin format began (two groups of four players, after first round elimination) and Australian Evonne Goolagong won.
1976
Australia Evonne Goolagong Cowney on the cover of SI during the Finals at LA Memorial Sports Arena.
1977
The tournament moves to Madison Square Garden and Chris Evert takes home the title.
1983
Evert at the Virginia Slims Championships at Madison Square Garden. Navratilova took home the title that year.
1992
No. 1 seed Monica Seles beats Navratilova 7-5, 6-3, 6-1 to win her third year-end title.
1992
Martina Navratilova was sad.
1995
Steffi Graf beat Anke Huber in five-sets (yes, the final was best-of-five for a few years) to win her fourth title.
1996
Gabriela Sabatini retired from the game at the 1996 WTA Finals.
1996
Kimiko Date Krumm also retired at the 1996 tournament. She would return to the tour years later and still plays at 43-years-old.
1999
Steffi Graf hung up her racket at the 1999 tournament and received...a gift.
1999
Lindsay Davenport and Martina Hingis met in the final for the second straight year and once again Davenport prevailed.
2000
Martina Hingis won her ninth title of the year, defeating Monica Seles in three sets.
2001
The Finals said goodbye to Madison Square Garden after a 22-year run and relocated to Munich, Germany.
2001
Serena Williams, making her tournament debut, wins the title after Lindsay Davenport withdraws before the final with a knee injury.
2001
An unhappy Davenport talks to reporters after withdrawing due to a knee injury she sustained in her previous match.
2002
Kim Clijsters stuns No. 1 Serena Williams, who had won three majors that year, to win her first WTA Finals title.
2002
The tournament moved back to America after a one-year stint in Munich, settling in Los Angeles.
2003
The WTA Finals has always served as a reunion of the game's legends.
2003
Clijsters and Hingis hanging out at the beach.
2003
Ever the stalwart, Martina Navratilova played doubles with Svetlana Kuznetsova
2003
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.
2004
The WTA Finals were sponsored by Porsche...
2004
...That's the only reason why this photo makes sense.
2004
17-year-old Maria Sharapova made her debut after winning Wimbledon that year.
2004
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.
2005
Amelie Mauresmo beats Mary Pierce in the first all-French final.
2006
Justine Henin wins her first WTA Finals title and finishes the year No. 1.
2007
In one of the most memorable finals every played at the event, Justine Henin beats Maria Sharapova 5-7, 7-5, 6-3.
2008
The tournament moves to Doha, Qatar for three years.
2008
The always combustible Vera Zvonareva made the final, but lost to Venus Williams 6-7 (5), 6-0, 6-2.
2008
It was Venus Williams' first year-end title.
2009
Serena and Venus Williams qualified for the event in both singles and doubles.
2009
But not in ping pong.
2009
Caroline Wozniacki came down with leg cramps.
2009
And in the first all-Williams final of the tournament, Serena came out on top.
2010
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.
2010
Elena Dementieva stunned everyone by announcing her retirement.
2010
No one was prepared.
2010
Kim Clijsters would win her last WTA Final title.
2011
The tournament moves to Istanbul, Turkey for three years.
2011
In her tournament debut, Petra Kvitova wins the title without dropping a set and finishes the season at No. 2.
2012
For the first time in WTA history, eight different countries were represented at the Finals.
2012
73,072 fans came out to Sinan Erdem Arena for the tournament, the largest attendance since 2000.
2012
Serena Williams extended her win-streak at the event to 10 straight matches en route to the title.
2013
The final staging in Istanbul.
2013
Serena Williams won her fourth WTA Finals title, beating Li Na in three sets in the final.

Contributor, SI.com Nguyen is a freelance writer for SI.com, providing full coverage of professional tennis both on and off the court. Her content has become a must-read for fans and insiders to stay up-to-date with a sport that rarely rests. She has appeared on radio and TV talk shows all over the world and is one of the co-hosts of No Challenges Remaining, a weekly podcast available on iTunes. Nguyen graduated from the University of California, Irvine in 1999 and received a law degree from the University of California, Davis in 2002. She lives in the Bay Area.