Women with the Most to Prove in Late Rounds of the 2015 Miami Open

Upsets have rocked the field in Miami.

Top-ranked women like Maria Sharapova, Caroline Wozniacki, Ana Ivanovic, Agnieszka Radwanska, Ekaterina Makarova and Victoria Azarenka were shown the door early, which leaves the remaining players a golden opportunity for a deep run.

Despite all that star power now gone from the tournament, there are still a number of viable contenders in the form of rising talents and established veterans. Knocking Serena Williams off her throne won't be easy, but if this event has proved anything, it's that no one should be considered safe.

Here is a look at some of the remaining women who have the most to prove over the final rounds of the Miami Open. A strong result here could set them up for much bigger dividends later this spring.

Sloane Stephens

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Just when you thought Sloane Stephens was out, she pulls you back in.

The 22-year-old American burst onto the scene in 2013, reaching the semifinals at the Australian Open and the quarterfinals of Wimbledon. She finished that year 12th in the world, and her stock couldn't have been higher. 

And then 2014 happened.

Last year was a nightmare for Stephens. She failed to advance past the fourth round at any of the majors and finished the season with a mediocre 21-20 record. More troubling than her results was the way she seemed to lack fire on the court. 

Stephens was determined to get back on track, and with the help of new coach Nick Saviano, she's slowly rounding back into the form that once had her labeled as the next female star. 

After a 2-4 start to 2015, things weren't looking much better. But at Indian Wells, Stephens earned hard-fought victories over Angelique Kerber and Svetlana Kuznetsova to reach the fourth round. She even pushed Serena Williams to three sets before eventually bowing out.

But that type of result was exactly what Stephens needed for her confidence heading into Miami. She's certainly made good on that form this week, taking out fellow rising stars Madison Keys and Belinda Bencic to reach just her second quarterfinal berth at a WTA Premier event.

With Simona Halep up next and a rematch with Williams looming, Stephens can get back on course in her mission to reach the top 10. 

Andrea Petkovic

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The last three years have been an enormous struggle for Andrea Petkovic.

When she broke through and reached the quarterfinals at three of the four majors in 2011, it was easy to peg the German as a rising star. She had both the talent and demeanor capable of winning any event.

But after rising to the No. 9 ranking at the end of 2011, injuries derailed her momentum. 

First, a stress fracture in her back sidelined Petkovic for months. Then, a bum ankle returned her to the shelf. By a cruel twist of fate, she then ruptured her meniscus and needed surgery. All that time away from the game shook her confidence as she sagged in the rankings.

There have been flashes along the way of the old Petkorazzi—as she's known on YouTube—but never sustained success. Petkovic is back up to No. 10 in the world with the help of her run to the French Open semifinals last year, yet she sits at just 10-6 on the year. 

Now is the time for her to build precious momentum heading into the clay-court season, where she has big points to defend. Already she's had an impressive week in Miami, toppling eighth-seeded Ekaterina Makarova in the fourth round for her first top-10 win in 18 months.

She'll face Karolina Pliskova in the quarterfinals for the right to potentially square off with Venus Williams in the quarterfinals. Both matches are winnable, and Petkovic desperately needs to perform well. If not, she'll be left searching for more answers.

Venus Williams

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Venus Williams just keeps going—and winning.

After many had written her tennis obituary, she's undergone a renaissance in 2015, soaring to an 18-3 record and a title in Auckland. As she nears another visit to the top 10, the 34-year-old is even in contention for a spot in the WTA Championships.

For Williams, that recent run of sterling form has surfaced again in Miami, and she's now in the quarterfinals after scoring wins over Samantha Stosur and Caroline Wozniacki. Her fitness, movement and shot-making are better than they've been in years.

While the seven-time Grand Slam champion may not need another title this week to boost her legacy, a strong finish could set her up well for a storybook run this summer at Wimbledon. Even if Williams stumbles in her next match, just making it this far has shown she can't be written off yet.

But a possible finals matchup against sister Serena has to be especially enticing for Venus in the short term. With her draw opening up, she has a great chance to reach that sibling showdown. 

Sabine Lisicki

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Wimbledon's pristine lawns are like a second home for Sabine Lisicki.

The German has reached the quarterfinals or better in her last five appearances at the event, including a runner-up finish in 2013. But away from the All England Club, she's too often played like a fish out of water.

Lisicki has never found much success on hard or clay courts. Her most notable result on either surface was a title at the Family Circle Cup in 2009. Her overpowering serves and attack-first mentality are well-suited to low-bouncing grass, yet those skills haven't carried over. 

She may finally, however, be adapting her game to other surfaces.

At Indian Wells, Lisicki hit her way into the semifinals, her best career result by far at any of the WTA Premier events. Though she fell in three sets to Jelena Jankovic, the 25-year-old took out Caroline Garcia, Sara Errani and defending champion Flavia Pennetta. That's not bad for a player without much of a hard-court resume.

In Miami, she hasn't slowed down. Lisicki booked a spot in the quarterfinals against Serena Williams after beating Julia Goerges, Ana Ivanovic and Errani (again), and she's up to No. 21 in the world.

But are her recent results just a flash-in-the-pan or the sign of a developing contender? Lisicki will be able to answer that question when she faces Williams in the next round. If Lisicki somehow survives that match, she would be well on her way to locking up the biggest title of her career. 

Simona Halep

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With her title at Indian Wells last week, Simona Halep has firmly established herself as a top contender on the WTA Tour. 

It's the biggest tournament she's won to date in her career, and her stock is soaring as she approaches the No. 2 ranking. So what else is left for her to prove?

That she can beat Serena Williams.

The two were slated to play in the semifinals of Indian Wells, but Williams had to walkover because of a knee injury. Halep took advantage of her free pass into the final and outlasted a stiff test from Jelena Jankovic for the crown.

Still, the Romanian's win comes with somewhat of an asterisk since she didn't have to face Williams. And she wanted that shot.

Halep could get that chance here in Miami, as she's slated to play Williams in a potential blockbuster semifinal. She's just 1-4 against the world No. 1, with her sole victory coming in the round-robin stage of last year's WTA Championships. 

For Halep, beating Williams would massively boost her confidence heading into the French Open, where she made the finals in 2014. Though she's known as a counterpunch artist, another trophy this week would be further proof that her style is more than capable of winning a Grand Slam.

All statistics courtesy of WTATennis.com unless otherwise noted. 

Joe Kennard is a Featured Columnist for Bleacher Report. 

Follow @JoeKennard.