Let's get the obvious out of the way: Who doesn't need a strong 2013 season? Those on the cusp of retirement need a strong year to justify soldiering on. Others must hit the brakes on a slide and get their careers back on track. Still others need a solid showing simply to remind pundits, fans and even themselves what they're capable of doing -- that they are still relevant and worthy of great accomplishments.
That said, here are six players in critical positions going into 2013.
[2013 Preview: Rankings movers and sliders]
Caroline Wozniacki: It took a strong push from Wozniacki at the end of the season to remain in the top 10, but it seems like ages ago that she was No. 1. The troublesome aspect of the Dane's 2012 wasn't just that she was passed by the likes of Serena Williams, Maria Sharapova, Victoria Azarenka and Agnieszka Radwanska. The problem is she spent the majority of the year playing well below her level, losing to players she spent much of her young career beating.
No one expected Wozniacki to defeat Williams or Sharapova on a regular basis -- though she finally notched her first win over Serena, in Miami -- but Wozniacki's stable game and competitive tenacity led to reliably consistent results in the past. That consistency went out the window. A crisis of confidence and lack of clarity in her game crept in. She went from a player who bagged six titles in both 2010 and 2011 to going trophy-less until Seoul in the fall. Back-to-back first-round exits at Wimbledon and the U.S. Open didn't help. The woman who sat atop the rankings for two years became an afterthought.
Bernard Tomic: Last year around this time, all eyes were on Tomic because of his game. Now, he's still grabbing headlines, but for all the wrong reasons. He began 2012 at No. 42 and had a solid run at the Australian Open, outlasting Fernando Verdasco and Alexandr Dolgopolov in two long matches before losing to Roger Federer in the fourth round. January would be as good as it got. He went more than three months without winning back-to-back matches, fell in the first round of Wimbledon (where he made the quarterfinals in 2011) and then mailed it in for the remainder of the year. They don't call him "Tomic the Tank Engine" for nothing. With his maturity and effort questioned, he's already been left off the Australian Davis Cup team for its first-round tie, and Tennis Australia has cut his funding.
And that's just the on-court stuff.
At 20, the reality is Tomic probably could have a few years of substandard results and still emerge as a very good player down the road. But that path is only feasible by being outside the spotlight, a luxury Tomic won't have given he comes from a tennis nation so starved for success. It's hard to feel sympathy for a player when you feel he might care less about his career than you do, so Tomic's mission for 2013 is to shake this "Tank Engine" business.
Jo-Wilfried Tsonga: There are times I'm convinced that all Tsonga wants in life is to be a solid journeyman. Get away from the pressure and expectation and just play his exciting brand of French tennis that is so enjoyable to watch but can yield few big-time wins. You know the type: They'd rather lose but hit the impossible, highlight-reel shot than grind out a win by executing the odds-on shot every time.
Tsonga had arguably a subpar season in 2012, when he went without a coach. Though he made the semifinals of Wimbledon and quarterfinals of Roland Garros, Tsonga played like he forgot he had the ability to upend any player at any time. Somewhere along the line he lost that belief that he could beat the Big Four and should be fighting for that famed No. 5 ranking. In that context, it's good to hear that he's hired Lleyton Hewitt's old coach, Roger Rasheed, a great motivator who knows a thing or two about trying to harness a wild and creative talent (his most recent coaching assignment: Gael Monfils).
Sabine Lisicki: The talented German looked primed for big things in 2012, having spent 2011 climbing from outside the top 170 to a career-high No. 12 and finishing at No. 15, thanks in large part to her first Grand Slam semifinal, at Wimbledon. With an opportunity to push into the top 10 and be a threat to win Slams, Lisicki put in a mediocre year. She had a five-match losing streak on clay and grass and then choked against Angelique Kerber in the Wimbledon quarterfinals, serving for the match in the third set. That loss left her sobbing and effectively ended her season. She went 1-6 the remainder of the year, which included first-round exits from the U.S. Open and two straight defeats to players ranked outside the top 50. She ended the year No. 37.
Lisicki, 23, is still young and has plenty of time to get her career right. But as Generation Next -- Azarenka, Wozniacki, Radwanska and Petra Kvitova -- matured and reached career milestones, Lisicki fell behind. She struggles with her fitness and is prone to long stretches of erratic play. Coached by her father, it's fair to wonder whether it's time to bring in a new mentor to shake things up. She's much too talented to be stuck outside the top 15.
Li Na: Paired with Carlos Rodriguez, there's lots to like about Li's potential in 2013. For my money she's the biggest underachiever in the top 20, a credit to her talent rather than undermining her accomplishments. The 2011 French Open champion still has the ability to win another Grand Slam on any surface -- she's an Australian Open finalist and two-time Wimbledon quarterfinalist -- but time is ticking. Li, 30, spent most of 2012 reminding everyone she wasn't going to be around much longer. Once she teamed up with Rodriguez over the summer, her tuned changed. She'd keep playing as long as she had the hunger and remained injury-free. So why does she need a successful 2013? Because I fear that anything less than a top-10 finish could mean she walks away from the game. Rafael Nadal: Nadal's second-half absence due to knee problems led to speculation from all angles. Was this the end? Was Nadal gearing up to embark on the final act of his career? Was this just a bump in the road? Nadal will give us more context once he returns. He can silence all the conjecture and doubt -- including his own -- with a strong comeback. That means going virtually undefeated on clay and winning his eighth French Open. Anything less than that, and there will be questions about Nadal 2.0.