Sanya Richards-Ross posted the fastest women's 400m time in the world this year as she won the title at the Michael Johnson Classic in Waco, Texas, in 50.18 seconds.
The performance by Richards-Ross, at the meeting on the campus of Baylor University, was 76-hundredths of a second better than the 50.94 that compatriot DeeDee Trotter posted hours earlier on Saturday in a victory at the Kansas Relays in Lawerence, Kansas.
The two are the only women to break 51 seconds so far in this Olympic season.
"I'm right there, right where I want to be," Trotter said.
Richards-Ross and Trotter were on the US team that won 4x400 relay gold in Beijing four years ago. Richards-Ross was favored for individual gold but settled for bronze behind Britain's Christine Ohuruogu and Jamaica's Shericka Williams.
In other events at the Kansas Relays, Bershawn Jackson ran the fastest time in the world this year in the 400m hurdles with a victory in 48.20sec.
Wariner delivered a strong first 200m before Rooney overtook him in the final stretch.
Dix, who earned 100m and 200m bronze at Beijing, overcame a sluggish start to win the 100m in a wind-aided 9.85sec.
With London looming, Dix said he was focusing on the process and not a potential podium finish.
"The last few years I've been focused on getting that gold medal and I ended up with bronze and silver (at the world championships)," Dix said. "So I'm not focused on that anymore. I'm just trying to be happy and run fast."
Felix anchored the Kersee All-Stars squad that also included Ginnie Crawford, Jeneba Tarmoh and Dawn Harperto a win in the 4x100 relay.
Source: AFP Global Edition