US Open of Tennis: The 4 Biggest Takeaways from Monday at Flushing

Day 8 at the US Open was a long one, so long in fact that Roger Federer and Juan Monaco didn't take the court until after 11:30 p.m.

Many of the day's matches ran for an extended period of time, with the wind also swirling away at the courts of Flushing Meadows. No player is safe at this point of the tournament, and the wind was just another factor causing the top seeds discomfort.

Regardless of the conditions, some great tennis was played on Monday, with no completely one-sided results during the matches.

Here's a look at the four biggest stories from Day 8 at the Open.

1. Jo-Wilfried Tsonga Is Fit

Jo-Wilfried Tsonga and Mardy Fish engaged in what would be Monday's most entertaining match.

Tsonga and Fish battled both each other and the elements, producing five great sets of tennis. Both players were striking the ball with tons of pace on the ground, while also playing stellar defense.

The most impressive facet of the match may have been both players' read of their counterpart's serve. The opponents combined for 15 aces in the first meeting between the two players.

Tsonga took the first set, but Fish fought back, taking sets two and three. He looked poised to take the match in four, but Tsonga got a second wind, and was able to take over the match midway through the fourth set.

Fish was unlucky to draw Tsonga, who I think will be celebrating another upset, this time over Roger Federer, in a few nights' time.

2. Serena Williams Does It Again

Serena Williams proved yet again that she's determined to storm through the draw and take the US Open title. 

Undeterred by her low ranking (29th), she has been excellent thus far at Flushing Meadows.

Serena controlled her match with Ana Ivanovic from start to finish, and has still yet to show any signs of rust from her long hiatus. She's striking the ball well, and her movement on the court is as good as ever, enabling her to turn defense into offense with one shot.

Ivanovic was no match for the 13-time Grand Slam champion, as the two were only on court for 74 minutes in the most one-sided match of the day.

Anastasia Pavlyuchenkova is the next victim for Serena, who is once again on her way back to the top of the women's game. 

3. Novak Djokovic Can Be Beaten

Did Novak Djokovic lose to Alexandr Dolgopolov on Monday? No, but he lost the aura of invincibility that surrounded him through the first three rounds of the tournament.

Djokovic played a long first set against Dolgopolov, nearly losing the set on numerous occasions in the tiebreaker. Djokovic stepped up his game in the next two sets to run away with the match, but he looked very vulnerable for a while.

The wind got in Djokovic's head, but Dolgopolov was the cause of some angst from the Serbian. Watching Djokovic mistime a fair amount of shots on Monday reminded me that the Serbian, winner of the Australian and Wimbledon titles in 2011, is still human. 

Djokovic is still the heavy favorite to win the U.S. crown, which would give him three out of four this year. But based on his performance against Dolgopolov, I wouldn't be surprised to see him drop a few sets along the way.

4. Caroline Wozniacki Shows Strong Mental Game

Caroline Wozniacki was yelling out in excitement—not anger—on Monday, having come back from a large deficit to knock out two-time slam champ Svetlana Kuznetsova.

Wozniacki trailed 4-1 in the second set after losing the first set in a tiebreaker. However, Wozniacki showed her much improved mental fortitude in this match, fighting back in the second set and dominating throughout the second set.

Wozniacki looked incredibly fit, making Kuznetsova move everywhere on the court, especially in the third set. Wozniacki still lacks aggression on her shots, which would pose a problem against Serena if the two were to meet in the semifinals. 

However, Wozniacki still has No. 10 Andrea Petkovic to worry about in the quarters. She needs to take this tournament one step at a time.