Serena Williams vs. Venus Williams.  It is one of the most famous rivalries in sports.  It is also the one in which there is the most familiarity between the two opponents.  Long before they ever turned professional, the Williams sisters were battling for bragging rights on the courts of Compton.  On Tuesday, a much bigger prize will be a stake, when the sisters meet once again to determine who will advance to the semifinals of the US Open.

There will be no surprises between this pair of combatants. They have met 26 times prior to this latest installment in their rivalry, and they each know their respective strengths and weaknesses.  And whether they choose to acknowledge it or not, they are also aware that it is younger sister Serena who is the clear favorite to get across the finish line.  She has won six of her last seven matches against Venus, and few would bet against her making it seven of the last eight.

One of the reasons Serena has been able to enjoy so much more success of late than Venus is that she is not dealing with the same health issues as her older sister.  This has enabled her to not only produce her best tennis on a consistent weekly basis, but to accrue the confidence that breeds future success.  A greater factor behind her winning record against Venus though is that she tends to do most things just a hair better.  Her forehand is more technically sound, and her serve – especially the second delivery – does not have a hitch like Venus'.  Furthermore, she is not as lanky and is built closer to the ground, which leaves her better equipped to add a little more sting to her shots when hitting on the run.  For all of these advantages, however, there is one area where Venus does hold an edge.  She is more comfortable in the forecourt than Serena and possesses greater reach when she gets to the net.  The 23rd seed has done an admirable job in the latter stages of her career to make a concerted effort to move forward, and she will need to do that on Tuesday if she wants to take Serena out of her rhythm and increase her odds of pulling off an upset.

But while the execution of their game plans will play an important role in determining the victor in this match, the crucially key component will come down to who mentally is better prepared to send the other packing. Ironically enough, this is the lone match in this tournament where the psychological pressure is arguably greater for Serena's opponent. 

Granted, Serena faces heavy expectations as the higher seed, who also has the winning record in this rivalry.  She has that added pressure that comes with trying to complete the calendar-year Grand Slam.  But it is because Serena is trying to achieve that feat that Venus potentially has a tougher psychological test in front of her.  She already knows that she has to red-line her game.  She is aware that her sister has defeated her six of the last seven times they have met and holds the overall winning record.  But she also has to face the fact that this time, her defeating Serena will not be the same as Serena defeating her.  If Serena defeats her, it will just be another loss at a major.  It will not be easy, but they have been there and done that many times.  If Venus defeats Serena, she has not just dealt her sister another loss at a major, but she is denying her the opportunity to do something that has not been done in nearly 30 years.  No doubt Venus wants to win, but if she gets in a position to do so, there have to be some questions as to whether or not she has the stomach to be the player to end her sister's bid for a calendar-year Grand Slam.

Venus definitely has the tools to end Serena's bid for history, but most do not foresee it happening.  Serena came out prepared and sharp against Madison Keys, and she is likely to do the same against Venus.  If she does, look for her to take one more step towards sweeping the majors in 2015.

From the moment the men's singles draw was released, there was buzz about a potential quarterfinal showdown between Novak Djokovic and Rafael Nadal.  The quarterfinals are now here, and Djokovic will be facing a left-handed Spaniard for the right to advance to the semifinals.  But it is not Nadal.  Instead, he will face Feliciano Lopez, who will be looking to continue his surprising run at this year's US Open.

There is no denying that Djokovic caught a break in facing Lopez in place of Nadal at this stage of the tournament.  Lopez has enjoyed a solid career.  He is currently ranked No. 19 and has been as high as No. 12.  He has four singles titles to his name and has been to the second week of a major on more than one occasion, including twice here in New York.  But his résumé is not nearly as impressive as Nadal's, nor Djokovic's for that matter.  The Serb firmly sits atop the rankings, has accumulated significantly more titles in his career, and is a nine-time major singles champion.  Obviously on paper, Djokovic is a heavy favorite in this upcoming match.

Differences in their career trajectories aside, Djokovic would still be considered the favorite against Lopez because of how their games compare.  The Spaniard enjoys the perks on serve that come with being a lefty, and he is able to go bigger on that specific stroke than Djokovic.  That said, his advantage in that department is slightly muted due to the fact that he is facing the best returner in the game.  And while the forehand of Lopez is typically more powerful than the top seed's, it is debatable that it will hold up under the pressure that Djokovic often puts on his opponents with his retrieving skills and ability to shrink the court.  Additionally, Djokovic is bound to pick on the Lopez slice backhand to quickly gain control of the rallies and dictate play.  Perhaps the only area where Lopez might find an advantage is with his play in the forecourt.  But even here, he is going to have to hit extremely effectively and choose his approaches wisely, or else Djokovic will regularly burn him at the net.

It is difficult to envision Djokovic feeling pressure on the pass, or any kind of pressure against Lopez for that matter.  As previously mentioned, he has had by far the more illustrious career and has been in this position so many more times than the Spaniard.  Djokovic owns an unblemished 5-0 record against Lopez as well, and he has dropped only one set in those previous five meetings.  In fact, the majority of the sets these two have played have not even been close.  In short, there is not a whole lot out there to give Lopez hope that he can turn the tables on the top seed.  But Lopez did have a noteworthy victory over Nadal in Cincinnati before coming to New York, and Djokovic has looked a bit rattled in his last couple of matches.  By all rights, the Spaniard also should have been out in the second round to Mardy Fish, and players who know they are competing on borrowed time have a history of raising the level of their games and becoming dangerous opponents. 

If Lopez does rise to the occasion, this could still evolve into a competitive affair even if it is not the Djokovic vs. Nadal clash so many had hoped they would witness.  But whether he brings his best or not, Lopez is going to need some help from Djokovic if he is going to pull off what would amount to a colossal upset.  The Serb has been too solid over the course of 2015, and it should take more than Lopez alone to stop him from reaching the final four.