Every tournament needs an early upset to jump-start things. After all, without the threat of a significant upset or faith that an underdog can make good, where's the fun? We might as well have a computer run probabilities, notch some random minor upsets along the way and move the seeds forward into the Round of 16. No, we need to believe that anything is possible when 128 players are placed into a draw. And, for the most part, we always get a reminder in the first few days of every tournament.
At the French Open it was Serena Williams bowing out in the first round to Virginie Razzano. At Wimbledon it was Lukas Rosol ousting Rafael Nadal in the second round. At the Olympics little Steve Darcis started the tournament with an upset over Tomas Berdych. And at the 2012 U.S. Open, 18-year old Laura Robson, ranked No. 89 in the world, ended three-time U.S. Open champion Kim Clijsters' career.
With that, the final Slam of the season begins in earnest, just in time for one of the most highly anticipated first week matches of the tournament.
Here's are a few matches with upset potential on Day 4 of the U.S Open.
Angelique Kerber (GER)  vs. Venus Williams (USA) (second night match, Arthur Ashe Stadium): Let's talk about Angelique Kerber, currently the best tennis player you've probably never heard of. At this time last year, the German was ranked outside of the top 100. She gets to the U.S. Open and has a stunning run to the semifinals, losing to eventual champion Sam Stosur. How do you say "fluke" in German? I don't know because Kerber, it turns out, wasn't a fluke. Since that semifinal run the 24-year-old has gone on an absolute tear, and while she has yet to win a major title, she's been the most consistent winner on tour, posting a tour-leading 54 victories this season (she won a total of 40 matches in her two previous seasons). Coming into 2012 she had never defeated a top-10 player. This year she's done it eight times, including wins over Serena Williams, Maria Sharapova, Petra Kvitova and Caroline Wozniacki.
All that is to say, Kerber is good -- very good, in fact -- and she's a name you need to know and take seriously. Venus Williams knows this. The two have played twice this year and Kerber won both matches. A powerful counterpuncher, Kerber hasn't dropped a set to Venus this year, beating her on clay in Madrid and on grass at the Olympics. One thing to keep an eye on here is the wind. This will be the last match at night on Ashe, and if the wind starts swirling, Venus' serve is in trouble. Both players were impressive in their first rounds and this will be Kerber's first trip to Ashe.
Mardy Fish (USA) vs. Nikolay Davydenko (RUS): No doubt, this isn't the Davydenko who reached a career-high No. 3 ranking in 2006 and was affectionately referred to as "PlayStation" by Juan Martin del Potro when the Russian went on to win the World Tour Finals in 2009. Now ranked outside the top 40, the 31-year-old Russian is clearly on the down slope of his career but that doesn't mean that top-five tennis still isn't in him. He beat John Isner in Nice in the spring and pushed Roger Federer to three sets in Rotterdam. Fish had a tough test against Go Soeda in his first match, winning 7-6, 7-6, 6-3. If Davydenko zones, Fish is in trouble.
Carla Suarez Navarro (ESP) vs. Agnieszka Radwanska (POL) (second match, Grandstand): I've been pretty vocal about my doubts regarding Radwanska's ability to make the second week in New York. She's carrying a shoulder injury and is otherwise in a slump of confidence since making the Wimbledon final. Talk to her for five minutes and you sense her physical and emotional exhaustion from what has been a breakout year. She is ripe for the pickin' here and while Suarez Navarro hasn't had consistent results this year, she has a history of being a solid hard-court player who isn't scared of the stage. The Spaniard with a beautiful one-handed backhand has reached two Slam quarterfinals in her career and made the fourth round at the U.S. Open last year.
Sloane Stephens vs. Tatjana Malek (third match, Louis Armstrong Stadium): Stephens' first-round win over Francesca Schiavone was a star-making turn, but can the American refocus and get the job done when the spotlight isn't on? By all accounts this should be an easy walk for the 44th ranked Stephens. Malek, a German qualifier, is ranked No. 141 and this will be only her second match against a top-100 player this year.
Marcel Granollers (ESP) vs. James Blake (USA) (fourth match, Louis Armstrong Stadium): Now 32, Blake is ranked outside the top 100 and his playing schedule these days is light. But scheduling him as the last match on Armstrong was a genius move by the USTA. With the rowdy night-time crowd behind him he might just have enough magic to knock out Granollers, a solid if not particularly spectacular Spaniard.Courtney's Pet Picks
: Milos Raonic (CAN) vs. Paul Henri Mathieu (FRA), Jack Sock (USA) vs. Flavio Cipolla (FRA), Sofia Arvidsson (SWE) vs. Ana Ivanovic (SRB), Sam Querrey (USA) vs. Ruben Ramirez Hidalgo (ESP), Tim Smyczek (USA) vs. Kei Nishikori (JPN), Yaroslava Shvedova (KAZ) vs. Roberta Vinci (ITA)