Allyson Felix (Getty Images)
Rio de Janeiro - US track star Allyson Felix cruised into the final of the women's 400m after topping qualifying times on Sunday.
Felix clocked a season's best of 49.67 seconds to win her heat ahead of Shaunae Miller of the Bahamas.
"It was good," Felix said. "I just wanted to put a solid effort down and try to make a run out of a good lane tomorrow."
Felix said she had worked on the second part of her race, adding that she was not concerned about late starts to the athletics programme here.
"I just wanted to bump up the intensity," she said.
"At this point I'm kind of used to (preparing for events). It's kind of been what we've been doing for a very long time."
Also qualifying for Monday's final are Felix's team-mates Natasha Hastings and Phyllis Francis, and double Jamaican threats Shericka Jackson and Stephenie Ann McPherson.
Making up the eight-woman line-up are Italian Libania Grenot and Ukraine's Olha Zemlyak.
But Britain's 2008 Olympic gold medallist and two-time former world champion Christine Ohuruogu, who finished in 51.22.
"I struggled to get into any sort of gear that could compete with these girls. I thought yesterday the old Christine was back but I think she only paid a fleeting visit," she said.
"She's gone. I have to be really honest. I know I'm a championship performer but it only works when I work, when I've got everything in my legs. I think it's been a tough year. There's so many aggravations and distractions and it does take its toll.
"In the middle of the year I got burned out. I think I tried too hard."
Felix, the reigning 200m Olympic champion, finished fourth in that discipline at the US trials, missing out on an Olympic berth to Jenna Prandini by one-hundredth of a second.
That loss ended Felix's hopes of becoming only the third woman in history to win both the 400m and 200m at the same Olympics after Valerie Brisco-Hooks of the US in 1984 and Marie-Jose Perec of France in 1996.