It was a record-breaking-day at the Rio Olympics on Sunday as Katie Ledecky beat her own best on the way to gold in the 400m freestyle with Adam Peaty in the 100m breaststroke and Sarah Sjostrom in the 100m butterfly following suit while Yuliya Efimova was jeered off as she aims to restore Russia's pride.

Katie Ledecky, targeting a rare 200m, 400m and 800m Olympic freestyle treble, surged home to touch the wall in 3min 56.46sec and felt "pure happiness" as she gazed at the scoreboard and contemplated her latest feat: smashing her own world record of 3:58.37 set in the Gold Coast, Queensland in 2014.

Upon seeing her time, she grinned broadly having achieved a goal she'd set herself back in 2013 of lowering the record in the event to "3:56 or better".

"To see 3:56 feels really good," said Ledecky, who now owns the six fastest times ever in the event and is one of only two women even to break four minutes.

For swimmer and two-time doping offender Efimova on the other hand, the situation looked bleak. She was jeered in the heats and at the 100m women's breaststroke semi-final with more verbal abuse likely to accompany her efforts.

The Russian, who was cleared to compete in Rio after a convoluted drugs case, triggered a chorus of boos when she was introduced and after the semi-final rival swimmers made their feelings known in no uncertain terms.

"I guess the whole point behind competition is we swimmers around the world, we train the hardest every day to be able to perform well and represent our countries and we train fair," said Defending Olympic breaststroke champion Ruta Meilutyte.

"And when something like that happens it's never nice and it's a little bit disrespectful," she added. "These are not the values of our sport."

Sarah Sjostrom became the first Swedish woman to win Olympic swimming gold on Sunday and she did it in style, setting a world record in the 100m butterfly.

Sjostrom touched in 55.48sec, lowering the mark of 55.64 she set at the World Championships last August in Kazan, Russia -- where she broke the record twice.

"I knew that when I had a good turn -- I came in with my hands perfect in the turn -- I knew it would be hard for the others to swim faster," Sjostrom said.

Silver medallist Penny Oleksiak of Canada and American bronze medallist Dana Vollmer were a study in contrast -- Oleksiak a 16-year-old Canadian and Vollmer the 28-year-old London gold medallist.

Neither had an answer for Sjostrom as Oleksiak clocked 56.46sec and Vollmer finished in 56.63.

Sjostrom, who was fifth in the 100m fly in London, has dominated the event since 2013.

Meanwhile, with the words of Muhammad Ali ringing in his ears, Adam Peaty obliterated his own world record to win the 100m breaststroke and provide Britain with its first male swimming gold medallist in 28 years.

The 21-year-old Englishman, showing no signs of nerves in his first Olympic final, blew away his opponents to win easily in a time of 57.13 seconds, slashing 0.42 off the previous world record he set in Saturday's heats.

None of the finalists could keep up with Peaty after he made a flying start off the blocks.

The race was already as good as over when he turned for home with a comfortable lead but he stretched out over the last lap to break his record and become the first British man to win an Olympic gold medal in swimming since Adrian Moorhouse won the same event at Seoul in 1988, more than six years before Peaty was born.

"We've just shown that even though we're a small country and we may not have the best facilities or whatever from a young age we can still pack a punch," Peaty said.