High jump world champion
qualified for London 2012 despite coming fourth at the US Olympic trials.
Only the top three are meant to qualify for the Games but third-placed Nick Ross did not have the "A" qualifying standard, meaning he missed out.
Williams, 28, missed three times at 2.31 metres after clearing 2.28 on his third attempt on a wet day in Eugene.
The American said: "The whole goal was to make London and now I am there I want to get on that podium."
2008 Olympics - high jump
Andrey Silnov (Rus) 2.36m
Germaine Mason (GB) 2.34m
Yaroslav Rybakov (Rus) 2.34m
He added: "These conditions were tough. It was really difficult for me to get in a groove and jump to my capabilities."
British high jumper
Robbie Grabarz has high hopes of gold
at London 2012, having recorded 2.33m at May's Diamond League meeting in Rome.
Jamie Nieto won the competition, Erik Kynard finished second and Ross was third, all at 2.28. Ross said: "It's bittersweet I didn't make the team. I'll definitely be on that podium again."
Five-time national champion Nick Symmonds dominated the men's 800m, winning in 1:43.92 seconds, while Alysia Montano claimed the women's race in 1:59.08.
Former world champion Bernard Lagat easily qualified in the men's 5,000m with a time of 13:42.83.