By Chris Oddo

(March 23, 2013) -- Serena Williams became the oldest No. 1 in WTA history when she defeated Petra Kvitova in the quarterfinals of the Qatar Open, and she could not hold back the tears when it happened.

Some thought it strange that a woman who spent years downplaying the rankings would emote so profusely upon reaching the milestone, but when you consider all that Williams had to go through to reach No. 1 for the sixth time in her career, it makes sense.

Read: Serena Reclaims World No. 1 Ranking in Doha

After a harrowing health scare the saw Williams hospitalized with a pulmonary embolism and a related grapefruit-sized hematoma in her stomach, Williams can't help but be blown away by the success she has achieved in the last year, given that she was fighting for her life--not her ranking--not so long ago.

It's given her perspective and that sense of perspective has helped Williams narrow her focus. She's playing with purpose now. In the past Williams has been criticized for not making the most of her immense talents, but the same cannot be said of Serena nowadays.

“I'm No. 1,” said Serena after her second-round victory at the Sony Open in Miami. “I'm pretty good at it still. So I feel like if I'm, you know, doing something well I don't want to stop, and I shouldn't stop. I don't have to play another match if I don't want to, but I'm having fun. I'm enjoying it.”

Read: Serena Williams Cruises in Miami Opener

Williams first ascended to No. 1 in July of 2002, and since then, despite missing time often due to injuries, she's held the top spot for 129 weeks, good for sixth all-time.

Now comfortably ensconced in the position, the 15-time Grand Slam champion has begun to gain a newfound respect for her place in the tennis pantheon. She hasn't spoken of it often, but these days it's clear that she'd like to rack up more Grand Slam titles. Lately, she's mentioned that she'd like to tie or pass Martina Navratilova and Chris Evert, who each own 18 Grand Slams. On Wednesday, she reitirated the notion, and didn't even rule out catching Margaret Court, who won 24 Grand Slams.

“I don't think I could...I don't know if I could ever top the No. 1 Margaret Court, but, you know, I don't know. It would be exciting and try to reach some of my fellow countrywomen that are ahead of me.”

Whether she can catch Court or not, the fact that Williams is setting her sights on building her legacy is a sign that Williams' current reign atop women's tennis could last for a while.

She may not be obsessed with the history books, but the recent period of self-reflection due to her own injuries and also the difficulties that her sister Venus has had to face with Sjogren's Syndrome, have certainly forced her to contemplate her mortality in tennis terms.

She may have another five great years left, but Williams is certainly a lot closer to the finish line than she was when she won her first Grand Slam in 1999 or ascended to the top of the rankings for the first time in 2002.

The history books, while hard to fathom for a 31-year-old who is still very much at the height of her powers, are now a part of Serena's internal dialog.

She was asked point blank on Wednesday if the history books matter to her.

“They don't normally,” Williams said. “But, you know, when you get close and are closer to a goal, you can't help but start thinking, 'Okay, I want to do history.' In retrospect I have made history already, so I just try to keep it going a little bit at a time.

Williams will continue her quest for history, and for a record sixth Sony Open title in Miami tonight, when she takes on Japan's Ayumi Morita in third-round action.

(Photo Credit: Mark Peterson/ Corleve)