Serena Williams and Simona Halep win in opening matches of WTA Finals

SINGAPORE -- If the first match at the WTA Finals was any indication, the upcoming week in Singapore will feature some fantastic shot-making, entertaining play and Slam-worthy intensity. If the second match was a barometer for the week, we're in for a long one. 

Two-time defending champion Serena Williams opened her campaign with a confidence-boosting 6-4, 6-4 win over No. 7 Ana Ivanovic. The match was the fifth meeting between the two this year, the most between any two players on tour. Serena showed no signs of the left knee injury that forced her to withdraw from the China Open mid-tournament, though she admitted to feeling the injury at times in the match. But behind 12 aces, 25 winners and just 14 unforced errors, Serena was able to withstand Ivanovic's offensive onslaught to impose herself throughout the match. The consistent pressure off the ground and on her returns unsettled Ivanovic, who said she felt rushed throughout the match.

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"She was putting a lot of pressure on my serve," Ivanovic said. "She served really well today I thought and created more pressure on my service game. I didn't feel my rhythm, so I was trying to make more first serves. In the second set I did that, but against Serena sometimes that's not good enough, and it wasn't good enough today." Ivanovic did well to stay level with Serena through both sets but faltered in the final game of each. Serving at 4-5 in the first set, Ivanovic double-faulted twice, broke at 15 and lost the set. Again in the second set serving at 4-5, she threw in a number of loose errors off the ground and broke again at 15 to lose the match.

"I felt pretty good," Serena said after the match. "I really felt like I don't really have anything to lose at this point. I just started practicing on Monday, so I feel like I just got to do what I got to do and do the best that I can.​" Both players agreed that Serena's serve was the difference in the match. When she injured her knee in Beijing, Serena said the injury affected her serve. On Monday night the serve was clicking. "I was pleased with my serve," Serena said. "Ana is a very aggressive returner, and I went really hard at my second serve. Didn't push them. Playing against her she'll hit winners, so I had to go for a lot."

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​The win extended Serena's streak to 16 consecutive matches won at the WTA Finals -- the second-longest winning streak in tournament history after Martina Navratilova's 21 from 1983 to 1986, and ​a streak she is reluctantly mindful of. "I'm aware of [streaks] because you guys make sure that I'm aware of them," she said. "So I just found out last time that I was 15 matches and I was like, 'Oh, boy, not another streak.' So now I'm 16 and, gosh, here we go again. We'll see how it goes."

While the first match of the evening featured a high level of tennis from both women, the second match between Simona Halep and Eugenie Bouchard was a decidedly one-sided affair. In a rematch of the Wimbledon semifinal, Halep won 6-2, 6-3 in just 68 minutes. While Halep's solid play contributed to the lopsided scoreline, it was hard to ignore Bouchard's 30 unforced errors and overall rustiness. Both women made their WTA Finals debut​.

The Evolution of Tennis Fashion: Ana Ivanovic

2005

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Braces! Nike! Separates! 17-year-old Ivanovic starts her climb.

2006

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Ivanovic makes her move to Adidas, where she'd end up signing a lifetime deal in 2010.

2006

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Wimbledon whites. Also note the Wilson racket.

2006

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Adidas opts for the string tank-top. Ah, the mid-aughts.

2007

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Ivanovic's first signature dress, which she wore to en route to her first Slam final at Roland Garros. She lost to Justine Henin in straight sets.

2007

Ivanovic at the U.S. Open. One of Ivanovic's freshest looks.

2008

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Adidas never did better than the bubble dress, which appeared in two Slam finals in 2008.

2008

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Ivanovic lost to Maria Sharapova in the 2008 Australian Open in the blue version of the Adidas bubble dress.

2008

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The iconic coral bubble dress launched a champion. Ivanovic won her maiden title at the French Open and took over the No. 1 ranking.

2008

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Let's forget the petal dress ever happened. An early example of Adidas trying too hard.

2008

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You're forgiven if you forget this look. Ivanovic was seeded No. 1 at the U.S. Open and lost to a qualifier in the second round.

2009

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Ivanovic was stuck with Adidas' attempt to "Go Greek" for over six months.

2009

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Swapping the colorways didn't save Adidas' "Greek Goddess" look.

2009

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Things get meshy at Wimbeldon.

2009

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The mesh continued in Tokyo. As Adidas would eventually learn, less is more.

2010

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Well at least they got the simple part right. This marked a turn towards a more modern look from Adidas.

2010

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The first great dress since her iconic 2008 dress.

2011

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The heavy zipper on the front was a distracting design choice.

2011

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A callback to the bright blue of her 2008 bubble dress.

2012

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Seemingly a simple design, but the dress never fit well on Ivanovic and the "X" pattern across the chest was unfortunate.

2012

Simon Bruty/SI

Ivanovic actually pulled off this neon-yellow look better than others did at the 2012 U.S. Open.

2013

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One dress, two colorways. Not feeling the faux-strapless look.

2013

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Ivanovic went all UCLA by the time spring came.

2014

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Still obsessed with greek draping and mesh, Adidas actually finally got it right at the Australian Open.

2014

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For Paris, Adidas kept the same silhouette and got rid of the draped neckline. Voila!

2104

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She wore this simple dress in both black and pink at the U.S. Open and it was easily her best look since 2008.

"I think today I had complete game, and just want to hit the balls very hard, to open the angles, and to play with good length," Halep said. "So I did. I served very well today. I'm really happy with my game."

Bouchard struggled to reign in her hyper-aggressive gamestyle. Halep's ability to patiently work the angles and get Bouchard to hit out of position paid dividends, as the Canadian failed to find her timing off the ground. Bouchard dismissed any concerns over a leg injury, but agreed that it impacted her practice schedule leading up to the tournament. 

It's been a year of first-time experiences and milestones for Bouchard, and the WTA Finals are yet another test for the 20-year-old. Usually you lose and go home, but here, Bouchard will have to get over the loss quickly to prepare for her next match on Wednesday. "I think it's totally weird," she said. "Because my coach is like, 'Okay, what time to you want to practice tomorrow?' Usually I take a day off after I lose. So that maybe makes you think less about the loss. I have to move on much quicker from it, which can be a good thing. Maybe makes the results of the match a bit less important in your head or something to worry about less, which is always a good thing."

Watch highlights from the Serena Williams and Ana Ivanovic match: