Who's More Likely to Be No. 1 at End of 2015: Serena Williams or Novak Djokovic?

Serena Williams and Novak Djokovic entered 2015 ranked No. 1. How likely is it that they end the year still on top?

Each won a Grand Slam last year and faced a number of ups and downs. Both finished 2014 by winning a year-end championship and playing in the International Premier Tennis League. 

They face similar challenges, but their priorities differ. Djokovic is trying to solidify his status as No. 1 and strengthen his resume. Williams knows she's playing in the final years of her career. She is chasing Grand Slams and trying to fortify her legacy.

After a roller-coaster season, Williams spoke with reporters about how important it was to finish strong.

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Yeah, it's been a really difficult year for me.  I don't think I've had such an up and down year.  I started out well with Brisbane; then didn't do well in Australia; then I did well again in Miami...I ended the year well. I had a couple injuries in the beginning of Asia, but I'm glad I came and I was able to end well.  So I think that was important.  How you start is how you finish, right? 

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Who wants it more? Probably Djokovic. How Williams and Djokovic manage their tournament schedule will signal just how important No. 1 is. After all, the quest for No. 1 is essentially a points race and Williams already seems less interested in chasing points. 

She skipped Brisbane (subscription required), where she was defending champion. Instead, she opted to play in the Hopman Cup, a quasi-exhibition mixed doubles tournament in Perth, Australia. With her focus on winning Slams, Williams must have noticed that although she won Brisbane in 2013 and 2014, she went on to perform poorly at the Australian Open those years. 

She won the Hopman Cup in 2003 (with James Blake) and 2008 (with Mardy Fish). She won the Australian Open in 2003 and reached the quarterfinals in 2008. Williams has won five Australian Opens. The last was 2010. 

Meanwhile, Djokovic, winner of four Australian Opens, is undefeated in finals in Melbourne. 

Mark Baker/Associated Press

Djokovic maintains a larger points lead over the No. 2-ranked player, Roger Federer, than Williams has over No. 2 Maria Sharapova.

Williams, however, has an easier path to holding onto her lead. That's because with the exception of the U.S. Open, Williams performed so poorly in Slams last year that she has fewer points to defend. 

She has her challengers, but Williams' toughest opponent will be herself. If she is healthy and focused, the rest of the field is in trouble. 

Djokovic has Federer, a healthier Andy Murray, Stan Wawrinka, Kei Nishikori, his French Open nemesis Rafael Nadal hoping to knock him off the top spot. 

It's early, but already Williams and Djokovic look less than solid. Ivo Karlovic upset Djokovic in Doha. Williams, meanwhile, struggled in her singles matches at the Hopman Cup. She needed an order of espresso to finish off Flavia Pennetta. Eugenie Bouchard beat her in straight sets and she needed two hours and 35 minutes plus a third-set tiebreaker to finish off Lucie Safarova.

This was supposed to be a more laid-back year for Williams. Especially now that she has that 18th Grand Slam. 

After securing her 18th Slam, Williams reflected on the troubles she had in 2014. In her post-match interview at the U.S. Open, she explained how perhaps she overtrained. She told reporters she was so disappointed about losing at Wimbledon because she trained so hard, sometimes six hours nonstop. 

 "At that moment I also realized I just needed to relax a little more. I put a lot of pressure on myself. I don't have to put pressure on myself, because like I said, I don't have to win another title. I always have my little 18 bracelet now. I'm good to go."

Similarly, Djokovic left Roland Garros dejected after another defeat to Nadal. A French Open title continues to elude him. Perhaps he too places too much pressure on himself. 

Djokovic is in his prime. Williams is facing decline. The blowout loss to Bouchard, multiple losses to Alize Cornet and early-round upsets prove she's already loss that air of invincibility. 

Clive Brunskill/Getty Images

Competitive to the core, Williams will try to hang onto the No. 1 ranking as long as she can. Yet her desire to win more Slams will come first. To stay healthy and hungry, she may need to skip more tournaments.

Meanwhile, Djokovic will fight like a mad dog to hang onto the top spot. After winning the ATP World Tour title, Djokovic told reporters how much he values the No. 1 ranking. 

"Well, right now I'm at my pinnacle in the career...I'm very motivated to keep on playing on a very high level.  So as long as it's like that, I'm going to try to use these years in front of me to fight for No.1 of the world and to fight for, you know, biggest title in the sport." 

Williams understands that whether she's ranked No. 1 or No. 25, she is considered the best. Her status as Greatest of All Time, remains debatable. 

One is playing to prove he's the best on tour. The other is gunning for greatest of all time. Because Williams can attain what she wants without remaining No. 1, she's less likely to make the ranking a goal. 

Djokovic is more likely to wind up No. 1.