Martina Hingis is a tennis legend. She won all five of her Grand Slam singles titles before she was 19 and is still the youngest champion at the Australian Open and Wimbledon.

She is already in the Tennis Hall of Fame, so it is easy to forget Hingis is just 33. (She turns 34 on Sept. 30.) She is younger than Venus Williams by a few months. She is just two years older than Serena Williams and a year and a half older than 2014 Australian Open champion Li Na.

But Hingis' last run at a major title was at the 2002 Australian Open where she lost to Jennifer Capriati in three sets of the championship match.

Now after two retirements, Hingis is back on the court and contending for the U.S. Open title -- as a doubles team with Flavia Pennetta of Italy.

"It feels like a really long time ago," Hingis says of 2002, shortly after she and Pennetta advanced to the semifinals. "It's a new moment, a new situation. I really enjoyed being out there. I really just hope to play as we've been doing so far and not think about what it is."

Hingis has won nine Grand Slam doubles championships with the 2002 Australian, partnering with Anna Kournikova, being the most recent.

In her late teens, Hingis dominated women's tennis. Along with her five Grand Slam titles and 12 Grand Slam final appearances, Hingis was ranked No. 1 in the world five times. Her 209 weeks as the world No. 1 are fourth all-time behind only Steffi Graf, Martina Navratilova and Chris Evert, and she barely held the spot after age 21. (Serena Williams is at 204 weeks as of Sept. 1, and will likely catch Hingis in the next month.)

"Some of the young kids, they don't remember me anymore," Hingis says with a laugh.

Hingis abruptly retired from tennis in February 2003 at 22 due to injuries. Hingis had surgery on her right ankle in 2001 before needing a left ankle ligament operation in 2002. The ankle troubles wore Hingis down to the point she walked away with 40 singles and 36 doubles titles to her name.

After an unsuccessful return in 2005, Hingis won three more singles titles and one doubles titles during a 2006-2007 run. She made quarterfinals appearances at three grand slams in seven tries. In late 2007, Hingis tested positive for benzoylecgonine, a metabolite of cocaine. Hingis appealed, arguing the small concentration of the test suggested tampering with the sample. However, at the end of the season, she was suspended two years from tennis.

After retiring again following the test, Hingis' career appeared to be over. From 2010 to the middle of 2013, Hingis participated in World Team Tennis and Legends events, but she did not reenter the professional tour.

In July 2013, at age 32, Hingis made the decision to return to professional tennis as a strictly doubles player. She paired with Daniela Hantuchova for the rest of the year, which included a first-round loss at the U.S. Open.

In early 2014, Hingis joined forces with Sabine Lisicki of Germany, who is ranked No. 27 in the world. As a wild-card entry, they won the Sony Open in Miami for Hingis' first professional victory in seven years.

In the second half of this season, Hingis has found a stable partner in the 32-year-old Pennetta, the current No. 12 in singles a former No. 1 in doubles. The two players have a veteran demeanor about them that make the partnership seem natural. At the podium the duo jokes about age and rest.

"Fresh?" Hingis says when asked about playing doubles without the simultaneous grind of singles. "It's nice to have a day off in between."

Although Pennetta is at the top of her game right now -- she advanced to face Serena Williams for a spot in her second straight U.S. Open semifinals -- she understands how special it is to play with Hingis.

"It's nice. In the moment when I don't have everything, she is there," Pennetta says of Hingis. "The same goes to her. The first match we played, I was like I don't know what to do because we didn't know each other really well. Now, we're getting better."

In the late 90s, Hingis was the arch nemesis to the American core of Venus Williams, Serena Williams, Lindsay Davenport, Monica Seles and Jennifer Capriati. She was a fierce teenage competitor who challenged the locals head-on at Flushing Meadows.

Today's Hingis comes with a different flavor. The Swiss national is more laid back and smiles on the court. For the last decade, Hingis has seemed lost, lacking the success she once had in her sport. Now, to a degree, the results are back, and she is having fun.

When asked about playing on the backhand side of the doubles court for a righty, Hingis bursts into laughter.

"I'm very happy she takes the forehand court," Hingis jokes.

"What do you play? Backhand?" Pennetta reenacts their communication.

"Every time I win on my serve with a forehand crosscourt, I think this is almost won!" Hingis says.

Although Hingis has aged, her mother is apparently still a diehard fan.

"I just came off the phone with her for 20 minutes because she's watching," Hingis says. "She's like, 'I don't know I still get nervous.' Like after 20 years -- watching doubles?"

Doubles is what Hingis has left and she seems comfortable with that.

"It's kind of a dream," Hingis says. "When I started playing again, this is definitely something I was hoping for with Flavia. I'm very happy to be part of this team."

The pairing's semifinal match is against No. 3 seed Cara Black/Sania Mirza. Unfortunately for fans, a potential Williams/Williams matchup with Hingis is no more. The sisters lost to Ekaterina Makarova/Elena Visnina, the No. 4 seed, in their quarterfinal.

But that also expanded the opportunity for Hingis/Pennetta to win a title.

"Right now, everybody probably thinks the door is open and everybody can win," Hingis says of the Williams/Williams exit.

If it happens, perhaps Hingis would display this trophy right next to those for her Grand Slam singles titles. As hard as she worked to earn those five, the grind to possibly earn a title while being on the verge of 34, is a different tale.

Even in doubles.

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