American swimming star Katie Ledecky smashed her own world record at the 400 meters freestyle event Sunday at the Rio Olympic Games.
The 19-year-old swimmer touched the wall in a time of 3 minutes 56.46 seconds, knocking nearly 2 seconds off the record to earn her first gold medal of the 2016 Summer Games.
Adam Peaty of Britain also set a world record for the men's 100 meters breaststroke with a time of 57.13 seconds to win gold. Earlier, Sweden's Sara Sjostrom broke the world record in the women's event.
The U.S. men's swimming team won a gold medal in the 4x100 relay. Michael Phelps, who gave the team the lead swimming a fast third leg, earned his 19th gold medal as the most decorated athlete in Olympic history. Americans regained the title in the event after the French took gold in 2012 in London. France came in second Sunday.
Defending champion Serena Williams of the U.S. battled high winds Sunday to reach the Olympic tennis second round, defeating Australia's Daria Gavrilova 6-4, 6-2, while organizers were roundly criticized for allowing play in conditions described as "ugly."
In women's doubles, Serena and sister Venus Williams had their hopes for a fourth gold dashed when they lost to Lucie Safarova and Barbora Strycova in the first round. It was the Williams sisters' first loss as a doubles team in Olympic competition. Together they won 15 previous matches and took the title in 2000, 2008 and 2012.
Rio Olympics Tennis: Serena Williams, of the United States, reaches for a return against Daria Gavrilova, of Australia, at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016.
In a major upset on the men's side, world number one Novak Djokovic of Serbia was ousted in the first round, losing in straight sets to Argentina's Juan Martin del Potro.
Winds up to 25 kilometers an hour forced a 90 minute postponement of Sunday's matches at the Barra complex in Rio de Janeiro. Top ranked Brazilian Thomaz Belluci, who opened at center court, said the competition marked "the first time of my life that I played in such terrible conditions."
At other events, media helicopters were grounded during the women's cycling competition, and rowers were ordered to stay off the water after competitors complained high winds that capsized a boat Saturday should have forced postponement Sunday as well.
In other action, reigning world champion swimmer Yulia Efimova of Russia was booed after winning her heat in the 100-meter breaststroke preliminaries, after serving a 16-month suspension for doping and then testing positive this year for the now-banned pharmaceutical meldonium.
Rio Olympics Swimming: Russia's Yulia Efimova competes in a women's 100-breaststroke heat during the swimming competitions at the 2016 Summer Olympics, Sunday, Aug. 7, 2016, in Rio de Janeiro, Brazil.
She and six other Russian swimmers were initially banned from the Rio games following reports from the World Anti-Doping Agency identifying a state-sanctioned doping scheme for Russian athletes. The Olympic International Committee reinstated her and several other high-profile Russian swimmers in the past week.
Day two of the Rio Games was also a day for the U.S. gymnastics women's team to make its debut.
Former Olympic champion Gabby Douglas received high scores in Sunday’s qualifying event, but will not compete in the all-around final to defend the gold medal she won in 2012. Although Douglas scored well, she still finished in third place. Teammate Simone Biles led the way scoring 62.366, two more points than teammate Aly Raisman who will compete with Biles in the all-around final. Only two gymnasts per country are allowed to compete in the final.
“I would have loved to go out there and defend my tittle, but I’m not disappointed. It’s been an amazing ride,” Douglas said.
The U.S. women's basketball team routed Senegal 121-56 in the opening round of competition.
Kosovo judo fighter Majlinda Kelmendi won the gold medal for the women's 52-kilogram division Sunday, giving her Balkan nation its first-ever Olympic medal. Kosovo, which became a country in 2014, is the 100th country to win an Olympic gold medal.
Rio Olympics Judo Women: Kosovo's Majlinda Kelmendi reacts after winning the gold medal of the women's 52-kg judo competition at the 2016 Summer Olympics in Rio de Janeiro, Brazil, Sunday, Aug. 7, 2016.
And Spanish cyclist Joaquim Rodriguez, who finished fifth in Saturday's competition, has announced his retirement, saying he has fulfilled a lifelong ambition to compete in the Rio games. The 37-year-old won three stages of the Tour de France in July, confirmed on Twitter that Saturday's race would be his last.