It's a clash of the top two seeds left in this week's Citi Open field as second seed Kei Nishikori battles third seed Marin Cilic. The two are meeting for the first time since Cilic beat Nishikori in straight sets to claim the title at the 2014 U.S. Open.

(2) Kei Nishikori vs (3) Marin Cilic

Nishikori has worked a simple route to the semifinals after struggling in his opener against James Duckworth. Over the last two rounds, Nishikori has won all four sets by an identical scoreline of 6-4 against Leonardo Mayer and Sam Groth. He weathered the storm against the power serve of Groth in the quarterfinals as the Aussie slammed in 16 aces during the match. Nishikori made Groth work though as he forced nine break points. The two seed would capitalize once in each set for all he would need. Lost in the mix was solid serving of his own as Nishikori won 71 percent of his service points. He saved all four break points he offered up. His serve isn't as flashy as a Groth or an Isner, but it has been effective this week with Nishikori winning 75 percent of the points on-serve.

Cilic has still not dropped a set this week in D.C. as he hung on for a tough 7-5, 7-6 (3) win over Alexander Zverev. Cilic looked as if he would make light work of the German as he raced out to a 3-0 lead in the first and second sets. In both instances, he would give the break back as Zverev kept fighting deep in each set. To Cilic's credit, he would regroup in the first and come away with a timely break to close the first set. In the second, he again showed his prowess in tie breaks this week as he won his fourth straight tie break.

The Croat's first serve was tough as nails, winning 86 percent of the points. Cilic had some issues getting that first serve in though at just 51 percent, which allowed Zverev 36 looks at his second serve. The unseeded teen took half of those points. Zverve was a bit sloppy on second serve again this match as he won just 42 percent of the points and he also committed nine double faults. At match's end, Cilic simply played slightly better in those key moments and that was the difference.

Ninth Career Meeting

When these two face off on Saturday, it will be the first time since Marin Cilic's first Grand Slam title at last year's U.S. Open. Cilic was in turbo beast mode the entire tournament on serve and Nishikori could do nothing to stop him. Cilic smacked one ace in a 6-3, 6-3, 6-3 win over Nishikori. It was Nishikori who had major service issues that day, winning just 58 percent of his service points. Cilic would break him five times out of eleven chances. Cilic saved eight of nine break points.

The U.S. Open marked the first time Cilic had beaten Nishikori since the 2012 U.S. Open. In between the two meetings, Nishikori won three straight against this week's third seed. On outdoor hard courts, the two have split six career meetings. Three of those have come at the U.S. Open with Cilic winning two of those three. The other three hard court meetings came in Brisbane in 2013, Chennai in 2011 and Indian Wells in 2008.

Fuel For The Summer

This is a huge spot for both players. There is no Andy Murray to go through in the final. They will face either John Isner or unseeded Steve Johnson. Cilic, in particular, would be rooting for Isner as he owns a 5-0 head-to-head record against the American. Nishikori isn't likely to have a preference, but did lose to Isner in straight sets at the Sony Open in Miami earlier this year. He could feel better prepped against either player after going against Groth.

This one would seem to hinge on Cilic's serve. When his serve is cooking, not even a quality returner like Nishikori will generate too many chances. Nishikori has been serving pretty well this week and he will need that to be the case again on Saturday. If Nishikori doesn't serve well, he has no chance. Expect a better effort in that category from Nishikori than what was put on display last Fall at the U.S. Open. Cilic has shown a couple of hiccups this week, but he has been able to fight back and win. This should be much more competitive than their last meeting, but this columinst will stick with the pre-tournament thought that Cilic can win the title.

Prediction: Marin Cilic in three sets.