By Alan Baldwin

RIO DE JANEIRO (Reuters) - Freestyle phenomenon Katie Ledecky made an impressive Rio debut with the fastest leg for the U.S. women in their 4x100 relay heat on Saturday.

The 19-year-old, who could win three individual freestyle events at the Games to add to her 2012 800m freestyle gold, had been uncertain for the team but her time showed why she had been selected.

Her splits were the fastest of the four team mates and, while not expected to race in Saturday's final, she hinted that she would be up for it.

Swimmers who compete in the qualifying heats also get medals if the team finishes in the top three without them in the finals.

World and Olympic champions Australia, with sisters Cate and Bronte Campbell powering the charge, were fastest with the U.S. women second and Canada third.

"I knew if I kind of stuck with her (Cate), and tried to keep an eye on her and get a little bit of a draft I could get up there," said Ledecky, who had not qualified for the individual distance at the U.S. trials.

"It's exciting, but the main goal was just to get a really good lane for us for the finals, just putting it all out there for the first race. "I'd love another swim but that's totally up to the coaches."

The fancied Dutch were only fifth fastest but rested triple Olympic gold medalist Ranomi Kromowidjojo with Inge Dekker appearing in the quartet instead.

Dekker, who was diagnosed with cervical cancer in February and had surgery in March, is taking part in her fourth Olympics.

The Dutch women won relay silver at the world championships in Kazan, Russia, last year with Kromowidjojo, Femke Heemskerk, Maud van der Meer and Marrit Steenbergen.

(Reporting by Alan Baldwin; Editing by Bill Rigby)