1) Usain Bolt v. Yohan Blake
Bolt remains the world record holder in the 100 and 200 meters, however, Jamaican teammate Yohan "The Beast" Blake is on his heels. The youngest ever 100-meter world champion also ran the second fastest 200-meter race of all-time last year when he blazed a 19.26. He also had Bolt staring at his heels in both the 100 and 200 meters at the Jamaican Olympic trials.
Blake is a 5-foot-11 speed demon who gets off the blocks quicker than Bolt, however, the 6-foot-5 reigning 100-meter gold medalist has the longer stride and most top line speed in the world. Unfortunately, Bolt has also been hampered by a right hamstring injury caused by a bad back.
Blake's advantage in the starting blocks is the reason that he is favored in the 100 meters while Bolt is the 200 meters.
Bolt is a naturally laid back competitor who has been known to rely on his natural talent. On the world's stage, it will be truly interesting to observe whether Blake's rigorous training has allowed him to surpass Bolt as the world's fastest man.
2) Ryan Lochte v. Michael Phelps
After winning eight gold medals in Beijing, it's not a lock that Phelps will be the fastest American in chorine this year thanks to teammate Ryan Lochte.
In an interview on the TODAY show Tuesday, Matt Lauer asked Lochte to write his own headline for the 2012 Summer Olympic Games. 'Ryan Lochte takes over' was the response he conjured up.
Lochte has reason to be confident. His record in the 200-meter individual medley was the first world record set since high tech suits, were banned. Conversely, Lochte abandoned his fast food habit after finishing behind Phelps during two events at the 2012 Games.
Meanwhile, Phelps isn't as beatable as the 26-year-old merman has openly talked about looking forward to life after competitive swimming and didn't train as ferociously as he did for the Beijing Olympics.
Originally, Phelps was on pace to race in eight events but he dropped the 200-meter free style meaning that he and Lochte will only race one another in the 200 and 400-meter individual medleys.
After Beijing, Phelps said he would never swim in the 400-meter IM, however, a lot can change over four years and as a result, Phelps will race Lochte in the grueling event Saturday. At the Olympic trials, Phelps beat Lochte by just 83-hundreths of a second in the four minute race.
Lochte is known for rocking diamond-studded grillz at the winner's podium but at the London Games, he'll be more focused on wearing gold around his neck.
3) Gabby Douglas v. Jordyn Wieber
Four years ago, Nastia Lukin and Shawn Johnson shared gold medals at the Beijing Games. In London, a fresh pair of American teens are expected to dominated the podium.
Although Wieber has dominated the gold medal count since 2009, Douglas is peaking at the right time. Nicknamed "The Flying Squirrel", Douglas won the all-around title at the Olympic trials on July 2 and received the highest all-around score in the World Championships, ahead of winner Jordyn Wieber, but her scores did not count because she was an alternate.
4) Roger Federer v. Djokovic
Every four years, tennis' best players participate in the unofficial fifth Grand Slam and of the 17 Grand Slams that Federer has won, he has yet to don a gold medal around his neck.
After Nadal pulled out of the Olympic Games due to an undisclosed injury, the door opened wider for Federer or Djokovic to win their first gold medals.
Less than one month ago, Federer defeated Djokovic and Murray to win his seventh Wimbledon title. While Murray is once again, the host country favorite, Djokovic and Federer have had some run-ins in recent years that would indicate they dislike each other greatly.
5) Spain v. United States
Barring a shocking upset, these two countries will meet in the gold medal game and stars Ricky Rubio, Pau and Marc Gasol have been talking about an inevitable rematch since the United States beat Spain in the Gold Medal Game at the Beijing Olympics.
This is seemingly the dawn of a golden age of team sports for Spain, whose Under-23 football team is expected to continue the country's run of dominance on the pitch. Meanwhile, the basketball roster is filled with NBA starters, All-Stars and champions. Ricky Rubio's torn ACL put a damper on Spain's festivities, however, Spain has point guard depth with Jose Calderon and ball handling wizard Sergio Rodriguez.
The United States has the depth and athleticism advantage but Spain has more size and like their football team is probably the best passing country in the world. The United State's sent a message in their 22-point win in an exhibition win over Spain, however, Marc Gasol will be playing the next time they meet and Spain won't be playing their cards close to their chest when the games actually matter and gold is on the line.
Honorable mention: China vs. United States (medal count)