US Open Tennis: 4 Biggest Takeaways from Sunday at Flushing

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Day 7 at the US Open is in the books and, for the most part, each match's anticipated winner came out on top.

Sixteen of 24 individuals that participated in Sunday's singles action were seeded, meaning the tournament's top guns were out to play on the last day of the first week.

Week 1 ended with four women making it to the quarterfinals, and the final 16 men in contention for the title decided. Of the 16 men remaining, only four are unseeded. All five of the top players on the men's side are still alive, while only two are still playing in the women's draw.

Here's a look at the top four moments to take note of from Sunday.

1. Donald Young Is Beginning to Mature

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Donald Young carried momentum from his win over No. 14 Stanislas Wawrinka to his match against No. 24 Juan Ignacio Chela, and proved he's ready to make a big step in his career.

Is Young ready to move into the top five? No, but he's ready to be a sleeper in majors, and even be seeded if he can keep up his intensity. His win over Chela pales in comparison to the one over Wawrinka, but he still beat a seeded player in the third round of a major.

Chela consistently hit shallow shots that Young was able to jump on, keeping the veteran Argentinian on the run. Young's only issue is his serve. He only averaged 101 miles per hour on first serves, which will not be good enough against the game's best.

Young's probably reached the end of his run, with Andy Murray being his next opponent, but he has many positive things to take from this year's Open.

2. Juan Martin Del Potro Is Overrated

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Don't get me wrong: Juan Martin del Potro is a great player, but he'll retire with one Grand Slam.

On Sunday, he lost to Gilles Simon, a quality player, in four tight sets.

Del Potro's run to the 2009 US Open was an amazing display of tennis, and his thrashing of Rafael Nadal and comeback against Roger Federer are two things you don't see too often. However, del Potro's form on his forehand will give him constant wrist issues throughout his career.

The Argentinian will linger between No. 10 and 20 for the better part of his career, with some appearances in the top 10. He'll have some big wins, but he won't string them together.

Sometimes I hear his name grouped in with the top four players as a tournament favorite and it confuses me. Yes, del Potro won a Grand Slam, but I don't think he should share the same ground with the game's elite.

Del Potro is a great player on tour, but his Grand Slam title gave him higher expectations than he'll be able to live up to.

3. Sabine Lisicki Was Not Ready for the Big Stage

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Sabine Lisicki's performance against Vera Zvonareva showed that she's not ready to break through just quite yet.

Lisicki has all of the shots to creep into the top 10, but she didn't have the mental game or consistency to do it at the US Open. Lisicki's ball toss was errant, and she was committing frequent first-ball errors, keeping her from getting any momentum against Zvonareva.

She'll have to continue working on her serve before she can post consistent results against the best players on tour. Lisicki is only 21 years old, so she'll have many more chances at slams.

The 2011 US Open was a good tournament for Lisicki, but she'll see better results in the future.

4. John Isner Looks Impressive Yet Again

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At the beginning of this tournament, I said John Isner would bow out to Marcos Baghdatis, citing his conditioning and passion as reasons.

Having watched Isner play in the first week, I'm very impressed by how far the big man has come since I saw him simply give up in an Atlanta final against Mardy Fish.

Isner is slapping aces left and right, while also crushing his forehand around the court. His presence at the net is frightening to any opponent he'll face in the future. His conditioning has yet to be tested, but I'd be startled to see him give up on a match in the second week of the US Open.

Isner is showing some of the skills I knew he had when I first saw him play in the NCAA singles championship. If he continues to work on his all-around game and conditioning, he could work his way toward the top 10.