Torres, 45, of Parkland, Fl., churned down the 50-meter pool in 24.82 seconds, coming in fourth. That was 32/100ths of a second behind first-place finisher, Jessica Hardy, and a mere 9/100th of a second after Kara Lynn Joyce.
Hardy, 25, and Joyce, 26, go on to compete in the 50-meter freestyle race in London. Coming in third was Christine Magnuson, also 26.
A chagrined but still smiling Torres said it was an emotional and rewarding experience to attempt another Olympics.
"I think this time around is going to be the most special to me because I think, mentally, it's been so tough the last couple years -- with having more bad workouts than good workouts, and going to meets and not being able to go faster at night than in the morning," she told reporters.
"She's bummed she's not going to London," Torres said of her 6-year-old daughter, Tessa, whom she was carrying in her arms.
Her improbable run has captivated many, especially those graying of hair and sagging of skin, who followed Torres long-shot attempt to join a team whose breakout female star likely will be a 17-year-old, Missy Franklin.
Physically, she battled reconstructive knee surgery, which prompted more than a year off from her otherwise rigorous training. Mentally, she coped with the illness and death last year of her coach, Michael Lohberg, from aplastic anemia.
"I was very emotional before my swim... I was thinking about Michael and, in July 2010, he had said to me, let's go for this," she said. "I really wanted to finish the story I started with him."
Torres leaves behind an Olympic career filled with records: She is tied with Jenny Thompson for the most medals won by an American female swimmer. Her five Games are the most for any American swimmer. And, she already became the oldest female swimmer ever to compete in the Olympics in 2008.
To accomplish that took extraordinary measures and an entire team of coaches, physical therapists, masseuses and others who helped condition, work and stretch her aging body into competitive shape, and then recover from all the punishment.
And just like that, it's over, something that Torres said probably would take a while to sink in.
"I'm going to enjoy some time with my daughter this summer," she said, "and cheer on the U.S. team."