Ryan Lochte beat Michael Phelps to win the 400-meter individual medley on Saturday night. Beat? Phelps finished fourth, off the Olympic medal podium for the first time since he was 15. But the American teammates might be on the same side Sunday, when medals will be handed out for the men's 400-meter freestyle relay.
It's the race that gave Phelps his most thrilling gold medal in Beijing four years ago, when Jason Lezak rallied in the last 25 meters of the anchor leg to overtake the French.
Among the other swimming highlights Sunday will be the final of the women's 100 fly. American Dana Vollmer set Olympic and U.S. records in the heats Saturday morning and qualified fastest in the evening semifinals. Also, fellow American Brendan Hansen will go for his first individual Olympic medal after qualifying in the eighth and final spot for the 100-meter fly.
The always-popular women's gymnastics gets underway at the North Greenwich Arena on Sunday as the United States seeks to claim its first team gold since the 1996 Atlanta Games.
The Americans figure to be tested by Beijing gold medalists China, as well as Russia and Romania.
Individual gold hopefuls Jordyn Wieber and Gabby Douglas lead a deep U.S. roster and are expected to be challenged in the individual all-around by Russia's Aliya Mustafina and Victoria Komova.
American McKayla Maroney is also a favorite to medal on the vault despite the aggravation of a toe injury last week.
The United States men's basketball team plays its first game Sunday, facing France in a preliminary group game. The Americans came into London as favorites, of course, having won four of the last five Olympic gold medals.
Argentina, which won gold in '04 to break the American strangehold, is in Group A with the U.S. and plays Lithuania on Sunday. Also, 2008 silver medalist Spain faces China.
There is potential for some quarterfinal positions to be locked up on Sunday when the men's soccer tournament continues with eight matches.
Both Uruguay and Japan can advance with wins over their respective opponents. Uruguay faces fellow Group A resident Senegal, while the Japanese continue Group D play versus Morocco.
In addition, the winner of a Group C bout between Brazil and Belarus would claim a quarterfinal spot if the group's other matchup of Egypt versus New Zealand ends in a draw.
Also on the schedule, Great Britain takes on the United Arab Emirates; Mexico and Gabon tangle; Korea does battle with Switzerland; and world and European champion Spain tries to avoid elimination, which would come with a loss to Honduras.
Sunday's tennis action is headlined by local favorite Andy Murray, the runner- up at Wimbledon this year, who returns to the legendary venue for an Olympic medal, facing Swiss Stanislas Wawrinka in his men's singles opener. Serbian star Novak Djokovic -- a five-time grand slam winner and the '08 bronze medalist -- is also playing Sunday, along with American Andy Roddick.
In women's singles, French Open winner Maria Sharapova gets her draw started with a first-rounder against Israeli Shahar Peer. Also playing Sunday are the top two players in the world -- Victoria Azarenka of Belarus and Agnieska Radwanksa of Poland. American Venus Williams, the 2000 gold medalist, also hits the court.
In doubles action, the defending gold medalists brackets are playing -- the Williams sisters, who have won two Olympic titles, and the Swiss duo of Roger Federer and Wawrinka.
Medals will be awarded in the women's cycling road race, a 140-kilometer event that will feature just 67 contestants. Nicole Cooke returns to defend her gold medal for Great Britain, but isn't among the top favorites. The Netherlands' Marianne Vos, German Ina Teutenberg, two-time reigning world champion Giorgia Bronzini of Italy, and 2008 silver medalist Emma Johansson of Sweden headline the contenders.
Two shooting golds will be handed out on Sunday, as the women compete in both the 10-meter air pistol and skeet events. Kimberly Rhode of the U.S. has an excellent shot at a medal in skeet, having won silver in the event at the Beijing Games.
South Korea has won the women's team archery event at every Summer Games since 1988 and placed first in the ranking round on Friday. The U.S. finished second in the ranking portion of the event.
In diving, the Chinese duo of He Zi and Wu Minxia enter the women's synchronized 3-meter springboard competition as the heavy favorites. They won the event at the 2011 world championships, where Wu -- a four-time Olympic medalist -- also won the individual 3-meter springboard world title and He took silver. Canadian Emilie Heymans is aiming for a fourth Olympic medal while diving with Jennifer Abel.
The first medals in men's fencing will be awarded on Sunday in the individual sabre. Expected to contend for the gold is German Nicolas Limbach and Alexei Yakimenko of Russia. Limbach has bested his potential counterpart in each of the previous three encounters.
A pair of Italians could also be a factor, 2004 Olympic champion Aldo Montano and former world No. 1 Luigi Tarantino.
Medals will be handed out in the men's 66kg and women's 52kg judo classes, as well as the women's 53kg and men's 56kg weightlifting groups.
The men's volleyball tournament gets underway, with the U.S. hoping for a successful defense of its 2008 gold, while women's field hockey makes its 2012 Games debut. The Americans will take on Germany to begin play.
Men's boxing continues with two weight classes: lightweight and welterweight.
Sunday's schedule is also expected to feature the second day group events of badminton, beach volleyball, equestrian, rowing and table tennis. Men's handball will also get underway after the women opened action yesterday.
Events set to get underway for the first time in these London Games include men's water polo, field hockey and sailing as well as canoe slalom.