After Thursday action in Flushing Meadows, the semifinals are set at the U.S Open. And as the tournament winds towards its conclusion, there is still compelling tennis left to play. Here is a look at the two matches on Thursday.

Federer Advances after Comeback

Second seed Roger Federer faced 20th seed Gael Monfils in the nightcap in Ashe Stadium. In a match filled with drama, it was Federer who prevailed in a tremendous comeback 4-6 3-6 6-4 7-5 6-2.

In the first set, with both players testing the tricky wind, a number of errors were struck by both. However, it was Monfils who adjusted first, striking timely winners and breaking Federer at 2-2. As the set continued, it was the quirky Monfils who appeared to have better feel, and he never relented on his serve, taking the set at 6-4.

In the second set, Federer looked out of sorts as he sailed a number of forehands long. Monfils capitalized, breaking in the first service game of the set. But in a key point, as he attempted to consolidate the break, the Frenchmen injured his ankle but decided to play on and held serve. Apparently unaffected by the injury, Monfils continued to attack Federer, maintaining his serve. Uncharacteristically, Federer appeared tight and gave away untimely unforced errors that led to a break opportunity as the 17-time Grand Slam champion served to stay in the set. Monfils took advantage and gained a two-set lead.

Suddenly, in the third, the momentum switched quickly in favor of Federer, who broke the Monfils serve early. Now, playing with a sense of urgency, Federer picked up the intensity looking to open up the set. However, Monfils did not back down, regaining his break back. But in the fifth game, not to be outdone and with the crowd now behind him, the No. 2 seed pressured the Frenchman with a bevy of volleys that earned him another break of service. Federer wrapped up an exceptional set of tennis, taking the third set.

In the fourth set, with the pair engaged in high-quality tennis, it was Federer gaining an early advantage. Showing that his game was not just flash, Monfils brought high-level intensity with his shot-making and broke Federer again. The frustrated champion showed rare outward anger afterwards, slapping his racket on the net. As play continued in the set, Federer was forced to hold serve to stay in the match at 4-5. The Frenchman gained two match points, but the veteran stepped up his game, fought off the points. and held serve to even the set. With the pressure now on Monfils, Federer found a crack in his serve and, aided by untimely double faults, secured the break. He would hold his own serve and force a deciding fifth set.

The hangover from failing to close out the fourth set carried over to the fifth for Monfils, who lost serve on his opening service game. Despite efforts to change the direction of the set, he could not stem the Federer tide. The 17-time Grand Slam champion closed out the match, staying alive for a shot at No. 18.

Cilic Sweeps Berdych

No. 14 seed Marin Cilic earned a semifinal appearance after he defeated sixth-seeded Tomas Berdych 6-2 6-4 7-6(4).

The Croatian, who has made a comeback from a doping suspension last year, finally lived up to expectations that many have had of the big hitter. On Thursday, he put Berdych on the defense from the beginning and never let his foot off the gas.

Behind his big serve and groundstrokes, Cilic took a quick lead and broke Berdych early in the first set. As the Czech struggled with his serve, Cilic came up with two additional breaks of service and won it with ease.

In the second set, Cilic fired seven aces and found one break on Berdych's serve, while the Czech could not make any headway into his opponent’s serve. The one break was all the 25-year-old would need, taking a two-set advantage.

In the third set, Berdych finally gained an advantage early, jumping out to a 3-0 lead. But it was a controversial double bounce call that changed the momentum of the Czech as he served at 4-2, 30-15. Berdych protested to chair umpire Louise Engzell that he got to the ball, but the call stood. He lost the game and continued his rant during the changeover.

The call appeared to affect Berdych as he dropped the set in a tiebreak, and Cilic advanced to his first US Open semifinal in straight sets.

Cilic credited his time away from the game during his suspension as a positive. “I matured a bit more, and I was working, day after day. I wasn't relaxing and doing nothing. So I think that helped me to improve physically. Also, it helped me to have enough time to put some new parts in my game, which are helping me to play this well now.”