"I knew I had to run fast," the former 400 metres world champion said after clocking 22.15 seconds to lead Allyson Felix, Jeneba Tarmoh, Tianna Madison and Carmelita Jeter into Saturday's final.
"I just wanted to execute well and get a good lane for the final," added Richards-Ross, who has already made the US team for next month's London Games by winning the 400 metres.
Only hew own 22.09 is faster this year.
Twice Olympic silver medallist Felix and Tarmoh, who are awaiting the resolution of their tie for third place in the 100, almost shared times again in the 200.
Felix won the third semi-final in 22.297 after Tarmoh had run a wind-assisted 22.298 in the first semi.
"Feeling good," said Felix as she was shepherded away from the track by coach Bob Kersee.
The pair should decide by late Saturday whether to hold a runoff or coin flip to decide which of them will compete in the even in London.
Madison finished behind Tarmoh in 22.33 with world 100 champion Jeter grabbed the last qualifying spot in 22.64.
Jeter won the 100 earlier in the trials with Madison second.
In a depleted men's 200, world medallist Wallace Spearmon led qualifying with a quick but wind-assisted 20.17 seconds.
"I didn't want to run that hard in the first round, but you have to do what you can to make the team," said Spearmon, who was qualified for a lane violation after finishing third in the 2008 Olympics.
He missed most of last season with a hamstring injury.
Neither Tyson Gay, Justin Gatlin nor Walter Dix, three of America's best sprinters, are competing in the 200.
"The door is open for anybody," said former world silver medallist Darvis Patton of his chances in the 200 after being sixth fastest.
Gatlin and Gay went 1-2 in the 100 and Dix has a hamstring injury.
Dix later said on his Twitter account he had been nominated for the US 4x100m relay pool, where he is expected to join Gatlin and Gay. Relay coach Jon Drummond confirmed the nomination to Reuters.
Jillian Camarena-Williams dominated the women's shot put, winning with a throw of 19.16 metres in the third round.
Michelle Carter and Tia Brooks also made the team for London.
Olympic silver medallist Hyleas Fountain enjoyed a comfortable lead in the women's heptathlon with 3,948 points after four events.
In the high profile men's 110m high hurdles, world champion Jason Richardson and world indoor winner Aries Merritt both clocked 13.13 seconds in the first round.
Olympic medallists David Payne and David Oliver also advanced.
Reigning Olympic champion Angelo Taylor and Games bronze medallist Bershawn Jackson paced men's 400 hurdles semi-finals.
Taylor ran 48.77 after Jackson cruised to 48.83 in the first semi.
"I'm one step closer to my dream," said Jackson, whose nickname is "Batman".