Novak Djokovic and Kei Nishikori meet for the 9th time when they face off in the Australian Open quarterfinals on Tuesday. This will be the first Grand Slam they have met at since Nishikori's stunning four set win over Djokovic at the U.S. Open semifinals in 2014.

How They Got Here

Novak Djokovic played one of the sloppier matches of his career against Gilles Simon in the fourth round. The Serb amassed an unheard of 100 unforced errors during the 6-3, 6-7 (1), 6-4, 4-6, 6-3 win for the top seed. Djokovic was visibly frustrated by Simon's penchant for putting the ball back into play deep into the middle of the court. The Serb's frustration was highlighted far too many times with ill-conceived and horribly executed drop shots. The shot is normally not a staple in the game of the world's top player. That is how much he hated being across the net from Simon two days ago. The Frenchman's game plan infiltrated Djokovic's service games too as the groundstroke wars began to wear on the Serb. That led Djokovic to dish out 18 break chances, 14 of which he was fortunate to save. That total of 18 was just one less than Djokovic had given out the entire season through eight matches and 19 sets. The positive of course is that despite Simon's tenacity and all those minuses in Djokokovic's game, the top seed was victorious.

Kei Nishikori found much less resistance from 9th seed Jo-Wilfried Tsonga in a highly anticipated match. It turned into the Nishikori show as the 7th seed whipped Tsonga 6-4, 6-2, 6-4. Nishikori was consistently into Tsonga's service games as he crafted 12 break chances and converted on five of them. The Frenchman may have been afflicted with some sort of back issue that required treatment, but Nishikori was in control regardless. Nishikori kept his unforced error count low with 25 to go with 32 winners. His serve was solid as he was broken just once on two chances. The 7th seed has dropped just one set through four rounds with that coming against Guillermo Garcia-Lopez when Nishikori was dealing with his own injury concern in the third round. The wrist problem that hurt him in that lost set did not seem to factor in whatsoever against Tsonga. That is good news for Nishikori ahead of the clash with Djokovic.

Nishikori's 2014 U.S. Open Win Seems Ages Ago

At the time, Nishikori's stunning 6-4, 1-6, 7-6 (4), 6-3 win over Novak Djokovic at the U.S. Open in 2014 was set to signal the Japanese star's arrival among tennis' elite. A few days later, some of the shine was taken off that win when Marin Cilic crushed Nishikori in straight sets to win the title. Since then, Nishikori has failed to live up to the lofty expectations that win put on him. Sure, he has now made three more slam quarterfinals in the past five slams since the U.S. Open, but he has not been back to even a slam semifinal since then. Most shockingly, he was booted out of the opening round of the 2015 U.S. Open by Benoit Paire as the 2014 victory seemed well in the distance after that loss.

Pure exuberance for Nishikori after beating Djokovic at the 2014 U.S. Open (Photo: Chang W. Lee/The New York Times)
Pure exuberance from Nishikori after beating Djokovic at the 2014 U.S. Open (Photo: The New York Times)

Head-to-Head

Since the 2014 U.S. Open encounter, Djokovic and Nishikori have met four times with the Serb dishing out revenge each time. Nishikori managed to win a set twice in those four meetings, but Djokovic hasn't allowed him to win more than three games in any of the other eight sets they have played. That includes four 6-1 sets and one at 6-0. To say the Serb has not forgotten that 2014 loss would be foolish. Nishikori's only other win in eight career meetings came indoors in Basel in 2011. This will be their third Grand Slam encounter with Djokovic winning the first at the 2010 French Open in straight sets and Nishikori of course evening the slam head-to-head with the U.S. Open win.

What To Expect

This match won't feature the multitude of grinding rallies of the Djokovic-Simon match. There will some of those exchanges. However, both Djokovic and Nishikori will prefer to use shorter exchanges to create favorable angles that they can use to their advantage. Expect a big portion of these exchanges to happen from the baseline where both are comfortable. Serve will be hugely important to the 7th seed in this match-up. Nishikori's serve has been much more prone to being broken over the years and Djokovic is the best in the business in return and defense. Djokovic, while at times susceptible serving, has improved in that category and is tough to beat when he gets his first serve in to win a high percentage of points.

Second serve especially will be a key statistic in this one. In their 2014 U.S. Open match, Djokovic was woeful in that department as Nishikori win 61 percent of those points. The man from Japan did well enough on his own second serve, winning half of those points, to keep himself afloat. Nishikori was also far more clinical in converting break opportunities as he took five of seven, while Djokovic could only cash in on four out of 13 chances.

The final thing to watch will be attitude. Djokovic was frustrated not just by his opponent, but likely by his own response to that frustration. A slow start by the Serb could result in some bad vibes for the top seed that could have a butterfly effect on this match. Still, Djokovic is a master problem solver on the court and no one seems more fit to handle a five set grind than the top seed. Nishikori would do well to find early success as Djokovic is difficult enough to beat in any situation, but certainly more so from behind. Look for Nishikori to have his moments and hit some of those ridiculous winners that only he cant hit. In the end though, Djokovic didn't survive Simon to see his run end here.

Prediction: Djokovic wins in four sets