Tyson Gay flew to the year's fastest 200m of 19.74 seconds at the US athletics championships on Sunday to set himself up for a World Championship sprint double challenge.
Gay, who notched the season's fastest 100m on Friday with a victory in 9.75, again demonstrated he is fit and ready to take on six-time Olympic champion Usain Bolt and his fellow Jamaican sprinters at the World Championships in Moscow on August 10-18.
Gay refused, however, to be drawn into any predictions as to how the US sprinters would stack up when the world's best gather.
"I am going to do the best I can," Gay said. "I can't speak for the other guys but I am going to go out there and give it my best."
As for his four days' work in Des Moines, Gay said he was satisfied.
"I wish my 100 was a little bit better. I have enough time to work on that," he said.
"My 200 was just an indication of my fitness. I'm definitely glad I was victorious."
Gay's 200m time eclipsed the 19.79 clocked by Bolt in Oslo on June 13 as the fastest in the world this year.
Gay powered through the curve and held on for the victory at Drake Stadium, with Isiah Young second in 19.86 and Curtis Mitchell third in 19.99.
Veteran Wallace Spearmon, a former world championships bronze and silver medallist, couldn't book his Moscow berth, finishing fourth in 20.10.
Gay, 30, has been hindered by a series of injuries since winning three gold medals at the 2007 worlds.
A hamstring injury derailed his 2008 Olympic campaign and 2011 hip surgery to resolve several chronic problems saw him sidelined for almost a year. He was shut out of the medals in the 100m at the London Games last year.
Weary after his 100m victory, Gay had said he would consider dropping the 200m if he felt it threatened his fitness.
Securing the double, and emerging healthy, was a mental and physical boost.
"A little bit of pride, a little bit of ego," he said of opting to go for it in the 200m. "I didn't want to give up on myself."
In the women's 200m, US collegiate champion Kimberlyn Duncan pulled off an upset, running down 2012 Olympic champion Allyson Felix to win in a wind-aided 21.80sec.
Felix seemed somewhat surprised to find herself second in 21.85 with Jeneba Tarmoh third in 22.15.
"She just ran me down," Felix said with a little laugh. "I felt like I had a lead coming off (the curve) and felt good coming down the home stretch and Kim came down and got me."
Felix is slated to run the 200m at the Diamond League meeting in Lausanne on July 4. After that she'll return home for some serious training before her bid to regain the world title she surrendered in Daegu in 2011. She had won world golds in 2005, 2007 and 2009.
Ryan Wilson was the upset winner of the 110m hurdles but world record-holder Aries Merritt did enough with his third-place finish to have a chance to add the world title to the Olympic gold he claimed last year.
Wilson won in 13.08 while David Oliver, the 2008 Olympic bronze medallist who dominated the event in 2010 before he was hit by injury in 2011, was second in 13.11. Merritt clocked 13.23 and Jason Richardson, who has a bye into Moscow as the reigning world champion, was fourth in 13.24.
Merritt, who hadn't raced until this week after straining a hamstring at the Shanghai Diamond League meet on May 18, said he had done what he set out to do, despite losing his rhythm at the fourth hurdle.
"I had to fight, because I knew I had to make the team," he said. "At that point, I probably lost all form and was ghetto-ing it down the track."
In other events on the final day, Olympian Duane Solomon won the 800m in a world-leading 1:43.27.
London Olympic gold medallist Jenn Suhr won the women's pole vault with a clearance of 4.70m to punch her ticket to Moscow, where the host team is likely to feature world record-holder Yelena Isinbayeva.
"I'm inviting as many family members that will go over to Moscow as I can to help cheer for me," Suhr said. "I think I'll be an underdog there."