Katie Ledecky can become the first Olympian since Debbie Meyer in Mexico City in 1968 to sweep the 200m, 400m and 800m freestyles
United States star Katie Ledecky bagged her second gold medal of the Olympic Games on Tuesday after powering to victory in the women's 200m freestyle.
Ledecky, who shattered the 400m freestyle world record in winning gold on Sunday, was second at the 100m mark but had moved into first at the final turn, holding off Sweden's Sarah Sjostrom with Australia's Emma McKeon claiming bronze.
Ledecky touched in 1min 53.73sec and is two-thirds of the way to a rare treble.
She can become the first Olympian since Debbie Meyer in Mexico City in 1968 to sweep the 200m, 400m and 800m freestyles.
The 19-year-old from suburban Washington DC burst onto the international scene with her 800m free triumph in London four years ago, and has steadily expanded her range.
But she admitted the 200m is her toughest challenge, and Tuesday's race was no exception, but she held on against a determined Sjostrom who came into the race buoyed by her own world record-setting win in the 100m butterfly on Sunday.
"That was a really tough race and it hurt really badly," Ledecky said. "I'm pretty sure that's the closest I've come to throwing up in the middle of a race.
"I'm just so glad I got my hand on the wall first -- it was all worth it."
Sjostrom, whose fly win made her the first Swedish woman to win Olympic swimming gold, was delighted with silver in 1:54.08.
McKeon, who led through the first 100m but was overtaken by both Ledecky and Sjostrom by the 150m mark, clocked 1:54.92.
Ledecky said the 200m remains a bigger mental challenge than the longer races she cut her teeth on.
"The 200 free is a much more stressful race than the 400 or the 800," Ledecky said. "It always just feels good when it's over. "Once I was ahead I knew I wasn't going to let it out of my hands.
"The last 50 I just had to dig deep, do my own thing and see if I could get my hand on the wall first."
Italy's Federica Pellegrini, who set the world record in 2009 in the era of the now-banned high-tech bodysuits, was fourth in 1:55.18 -- ahead of China's 2014 Asian Games champion Shen Duo.