Madison Keys

Since winning her first WTA Tour match shortly after turning 14 in 2009, Madison Keys has worked her way up the world rankings, peaking at No. 9 entering this year's U.S. Open.

But if you're not all that familiar with Keys, it's because she is still looking for that breakthrough win at the U.S. Open. It just might come Sunday -- the last Sunday for American families to crowd around their TVs before the NFL season -- when she faces former No. 1 Caroline Wozniacki in the fourth round.

In the third round, Keys came back from two breaks down in the third set to hold off 18-year-old Japanese upstart Naomi Osaka, 7-5, 4-6, 7-6(3). But winning an afternoon match on a Friday is a lot different than winning on the Sunday night of Labor Day weekend, particularly against someone like Wozniacki, a two-time U.S. Open runner-up with a big fan base.

"I think the crowd will be more divided seeing as she's a finalist, but I think I will have plenty of support," says Keys, who turned 21 in February.

Madison Keys

Her biggest win so far came at the 2015 Australian Open, when she beat Venus Williams in the quarterfinals before losing to Serena in the semis. She reached the quarterfinals at Wimbledon in 2015, has made it to the fourth round in the past four majors and is fresh off a fourth-place finish at the Olympics.

Playing with power reminiscent of the Williams sisters in their younger days, Keys has Grand Slam champion potential. With height and a wingspan similar to Venus, Keys has serving ability that is among the best in the sport. After beating Keys in the final of the Italian Open in May, Serena told her, "I'm so proud of you, and you're going to be number one for sure."

Maybe a win Sunday against Wozniacki will turn out to be a turning point, if Keys ever reaches the top spot. Thomas Högstedt, who used to coach Wozniacki (as well as Maria Sharapova, Li Na, Simona Halep and Eugenie Bouchard), is now working with Keys. Her previous coach was three-time Grand Slam champion Lindsey Davenport from 2014-15.

The hype will be real, the stadium (likely with a closed roof) will be loud and the result will be meaningful for both players. With No. 3 seed Garbiñe Muguruza out of their quarter of the draw, both players have a clear shot at the semifinals.

While Keys touted her consistency after the Osaka win, Wozniacki has struggled this season, missing the French Open and losing in the first round of both the Australian Open and Wimbledon. She has battled an ankle injury most of the year, and after ending 2015 at No. 17, Wozniacki has dropped all the way to No. 74.

As for the pressure of playing Wozniacki, Keys has already came back from a set and a break down in the first round against No. 60 Alison Riske and 5-1 down in the third set against Osaka. In both matches, Keys was two points away from being sent home.

"I'm never giving up and I'm fighting to the very end," she says. "That's something to pat myself on the back for. But also definitely going to sit down later and work on some things for the next round because I don't want to be two points from losing again. [I'm] really looking forward to trying to have straightforward matches."

Keys is a heartland girl, born and raised in Rock Island, Illinois, along the Iowa border. She smiles on the court, says thank you to the media and stops for selfies with fans. She is a favorite among those who meet her, but a sponsor is not about to make Keys the face of its product based on her personality alone.

"Lately, I have just been taking lots of naps and watching movies," she laughs when asked what she does off the court. "Normally, I like to hang out with my friends and family. I really enjoy baking, which is tough on the road. So whenever I'm home, I feel like I'm constantly in the kitchen."

-- Follow Jeffrey Eisenband on Twitter @JeffEisenband.