Katinka Hosszu of Hungary reacts after setting a new world record in the women's 400m individual medley final on Saturday. [Photo/Agencies]

Katinka Hosszu filled a glaring gap in her resume on Saturday by making her first Olympic medal a gold - and with a stunning world record to boot.

The Hungarian shattered the world record in the 400m individual medley, seizing control from the start and winning in 4 min 26.36 sec.

She eclipsed the previous record of 4:28.43 set by China's Ye Shiwen en route to gold in London four years ago, when Hosszu was relegated to fourth.

"Coming to Rio, I wanted to do the best I can, and I did," said the five-time world champion. "In London, I was under pressure, I was nervous before the final, I was preoccupied by the idea of what would happen if I didn't win.

"And I did not want to live through this again here in Rio," added the 27-year-old, who built her confidence up by swimming the second-fastest time ever in the heats. "I was confident. Today, I had a great time. I know I can go faster; going faster is what brings excitement for me."

At the 300m mark, Hosszu was move than five seconds under world-record pace, and she broke Ye's mark by 2.07 sec.

Hosszu was already celebrating when Maya DiRado of the United States finished second in 4:31.15, with Spain's Mireia Belmonte claiming bronze in 4:32.39.

For Hosszu, known as the Iron Lady for her grueling schedule, the victory was especially sweet. She had captured nine medals - including five golds - at the world championships but had never won an Olympic medal. She defiantly pumped her chest before breaking into a huge smile.

"I've been chasing that world record for some time," she said. "I knew I could go faster, but I didn't think I can go this much faster."

"I honestly didn't even see her, she was so far ahead," DiRado said of Hosszu.

Hosszu will have plenty of chances to expand her collection of Olympic medals in Rio de Janeiro. She has also entered in the 200m medley, the 200m butterfly and the 100m and 200m backstroke.

"I know I have some more races to go and I will have some more fun," she said.

Sister act

Australia turned to the best sister act in swimming to hold off a US team anchored by Katie Ledecky.

Cate and Bronte Campbell carried their squad to victory in the 4 x 100m freestyle relay on Saturday night, with little sister Bronte snatching the lead from Dana Vollmer on the third leg and big sister Cate pulling away from Ledecky on the final down-and-back for a time of 3:30.65.

The Aussies broke their own record of 3:30.98 set two years ago and defended their gold medal from the 2012 London Games.

"This one was different because it was expected," Cate Campbell said. "It's always a lot harder to do something when it's expected."

Also, Japan's Kosuke Hagino ended US dominance in the men's 400m individual medley, while Australia's Mack Horton took down Sun Yang of China. Horton clocked 3:41.55 to hold off a feverish challenge from 2012 gold medalist Sun, who briefly looked to have the Australian beaten on the last lap but had to settle for second in 3:41.68.