Gold for Phelps as world records tumble in pool

US swimming legend Michael Phelps extended his record gold medal tally on Sunday, crowning a record-breaking day of drama at the Olympic Games.

Phelps, the most decorated Olympian of all time, produced a stunning second leg to inspire the United States to victory in the 4x100m freestyle relay.

The 31-year-old - who has now won 19 gold medals, 23 overall - roared with delight and hugged his team-mates after they came home ahead of defending champions France in silver, with Australia third.

It was a fairytale moment for Phelps, who came out of retirement for one last crack at the Olympics after battling his personal demons during a stint in rehab.

USA's Michael Phelps smiles after team USA won the Men's 4x100m Freestyle Relay Final during the swimming event at the Rio 2016 Olympic Games at the Olympic Aquatics Stadium in Rio de Janeiro on August 7, 2016.  (AFP)

The American quartet's display capped a superb night at the Maria Lenk Olympic Aquatics Centre which saw three world records broken.

Phelps's fellow prodigy Katie Ledecky was among the biggest winners, obliterating her own world best in the in the 400m freestyle on her way to gold.

The 19-year-old touched the wall in 3min 56.46sec, taking nearly two seconds off her previous record.

Ledecky is bidding to become the first Olympian since Debbie Meyer in 1968 to win the 200m, 400m and 800m free in the same games.

Britain's Adam Peaty set a new global best with a win in the men's 100m breaststroke after Sweden's Sarah Sjostrom had also broken the record in the women's race.

"It's surreal. It was crazy. It's amazing and I probably won't be able to sleep tonight," Peaty said.

The spellbinding action in the pool brought the curtain down on another day of drama where 14 gold medals were shared out.

Among the most popular winners was the hard-as-nails 25-year-old judoka Majlinda Kelmendi from Kosovo, which only gained status as an Olympic nation in 2014.

Kosovo's Majlinda Kelmendi celebrates after defeating Italy's Odette Giuffrida during their women's -52kg judo contest gold medal match of the Rio 2016 Olympic Games in Rio de Janeiro on August 7, 2016. (AFP)

The 25-year-old sank to her knees in tears after out-grappling Italy's Odette Giuffrida to win by yuko in the women's 52kg final.

The win makes Kosovo the 100th country to win an Olympic gold medal.

"I have always wanted to show the world that Kosovo is not just a country that has gone through war," Kelmendi beamed with the Kosovo flag draped around her shoulders.

"We have survived a war. There are still kids who don't know if their parents are alive, don't have anything to eat or books to go to school. So the fact of becoming Olympic champion is just huge for all of us."

Djokovic, Williams sisters out

A turbulent second full day of competition began with strong winds wreaking havoc at several Olympic venues.

The entire day of rowing was called off after gusts churned waters making it impossible to row. Strong winds also delayed play at the tennis venue, which saw a slew of upsets when action resumed later.

The biggest casualty was world number one Novak Djokovic, bounced out in straight sets in the opening round of the men's singles by Argentina's Juan Martin del Potro, losing 7-6 (7/4), 7-6 (7/2).

It was an unexpected win for del Potro, who has struggled with wrist injuries in recent years.

"It was an amazing match for me. I didn't expect to win tonight as I know the situation with my wrist," said del Potro.

In the women's doubles, Venus and Serena Williams' long reign as champions came to an end when they lost to Lucie Safarova and Barbora Strycova in the first round.

"It was what it was. We have a chance to compete for our country and did the best that we can. We had a blast out there," said 34-year-old Serena after the 6-3, 6-4 defeat.

The women's cycling road race was won by Anna van der Breggen, who overcame the shock of seeing team-mate Annemiek van Vleuten lying stricken on the road after a horrific crash to win gold on Copacabana beach.

There was more disappointment for hosts Brazil in the Olympic football tournament, who were booed off for a second straight game after a 0-0 draw with Iraq.

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