By Andrew Downie

RIO DE JANEIRO (Reuters) - It is a measure of the U.S. dominance in the women's 100 meters hurdles that even with the world record holder absent the Americans are still favorites.

Brianna Rollins came off a couple of poor seasons to run 12.34 seconds and beat favorite Kendra Harrison in the U.S. Olympic trials.

Harrison responded by running a scorching 12.20 seconds in London's Diamond League meeting last month – beating the 28-year-old world record held by Bulgarian Yordanka Donkova.

U.S. women have filled five of the nine medal positions since Athens and ahead of the U.S. trials in Oregon in July, nine of the year's 10 best times were recorded by Americans.

Rollins acknowledged the U.S. strength in depth and said it boded well for medals when the competition starts on Tuesday.

"I think our trials system is a good system, it's a fair chance we all get," said the 24-year old from Miami. "It's unfortunate that Kendra can't make the team but she bounced back in London and broke the world record."

"It's most definitely one of the toughest teams to make," Rollins told reporters. "It could have been any one of those girls that made the teams.

"But I made the team, I worked really hard and it's something I truly, truly wanted to accomplish this year so I had my eyes on the Olympic trials and the Olympics games all season."

Some are predicting the Americans will sweep the podium in Rio but Rollins played down those expectations.

"I try not to put any pressure on myself,” she said. "I just try to just believe in what I've doing, I've been training all year for this moment, and this is what I do. So just having faith in my coach, and trusting the whole process will get me throughout this Olympic Games."

(Editing by Alison Williams)