Andy Murray and Angelique Kerber overcame dominant players last year to take their respective No. 1 rankings for the first time in their careers. However, they could both lose the top spot at the 2017 Australian Open, which gets underway Monday, January 16.
So which one of the newly reigning players is most likely to leave Melbourne, Australia, still ranked No. 1?
Both Murray and Kerber will be seeded No. 1 at the event for the first time in their careers.
Still, Novak Djokovic and Serena Williams remain the oddsmakers' favorites to win the tournament. Having overcome two of the most dominant players in tennis history, can Murray and Kerber solidify their holds on the top spots or will one or both of them cave under the weight of expectation?
Right now, Kerber has the larger lead over the second-ranked player. Williams trails Kerber by 1,795 points. However, Kerber is playing at Sydney and could further pad her lead. She has 2,000 points to defend at the Australian Open. Williams has 1,300 to defend.
Meanwhile, Murray has a slim 780-point lead over Djokovic. But unlike Kerber, who is defending champion at the Australian Open, Murray was runner-up.
Murray and Kerber each rose at a time when Djokovic and Williams seemed unstoppable, with each having won three Grand Slam titles in 2015.
Johnette Howard of ESPN wrote that despite that dominance, somehow "over the next 12 months, Scotland's Andy Murray and Germany's Angelique Kerber gave everyone a lesson on what it takes to thrive, not just survive, in the time of legends."
Murray is thriving among more legends than Kerber. In fact, Williams has won more than three times as many Grand Slams (22) as her sister Venus Williams (seven), who is No. 2 among active female players for most Slams won.
Murray has been the weakest link in the Big Four, which includes Roger Federer (17), Rafael Nadal (14) and Djokovic (12). Stan Wawrinka has three Grand Slam titles, the same amount as Murray.
But Wawrinka has never been ranked No. 1. By adding that to his resume, Murray could make a stronger case for membership in the Big Four. Holding onto the ranking would make his case even stronger.
After the defeat, Murray told reporters, "I still think I have a chance of winning the Australian Open after tonight. I don't think that changes. It's disappointing to lose for sure. I have a chance to win the Australian Open still."
The win ended Murray's 28-match winning streak and served notice that despite coaching changes, Djokovic remains the player to beat on the tour.
The same is true for Serena, no matter how poorly she played in her second-round loss at Auckland, New Zealand. She committed 88 unforced errors in brutal windy conditions.
Kerber doesn't put much stock in pre-Slam warmups. She told reporters in Brisbane, "I think Grand Slams are always completely different. Actually, doesn't matter how you play before. I mean, you can play very well the weeks before and then you are going to the Grand Slams and it's different."
Indeed, the previous two seasons, Serena began the year without any official match play, although she had competed in exhibitions.
One of the reasons Kerber was able to surpass Serena was that she played more tournaments. The Aussie Open will be her third tournament this year, Serena's second. Unlike Djokovic, who badly wants the No. 1 ranking, the American is focused on winning Slams. Her skipping the Asian swing and the year-end WTA Finals the past two years allowed Kerber to amass far more points.
It's all about the points race for Kerber and Murray.
Both face difficult fields with proven champions and hungry up-and-comers. However, the WTA field is far more depleted right now.
Maria Sharapova is serving a drug suspension, while two-time Australian Open champion and former No. 1 Victoria Azarenka recently gave birth to her first child. Former No. 1 and 2008 Aussie Open finalist Ana Ivanovic retired, and two-time Wimbledon winner Petra Kvitova is out recovering from a knife attack. Madison Keys, the youngest player in the Top 10, will miss the tournament with an injury.
The competition is simply stiffer for Murray right now. He has far more pitfalls awaiting and a much smaller lead going into Melbourne.
Kerber has fewer hurdles to clear, but unfortunately for her, the biggest threat to her is playing for history.
Still, Kerber's win at the 2016 U.S. Open already took her out of the one-hit-wonder category. She's the real deal, and despite far less experience in the spotlight than Murray, Kerber has a stronger grip at No. 1.