"I had a blast out there," said the 29-year-old Rupp, who now aims to make the U.S. team in the 10,000 metres in July and double at the Rio Games a month later.
"It's definitely possible. There is plenty of time in between to recover," said the U.S. 10,000 metres record holder, who became only the second American to win the trials in his first marathon after steeplechaser George Young in 1968.
The 10,000 metres comes first in Rio with the marathon following eight days later.
Keflezighi became the oldest U.S. runner ever to make an Olympic team as he took second in 2:12:20 to qualify for his fourth Games.
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"To come back as a 40-year-old to make it, I have been blessed more than you can ever imagine," said the 2014 Boston Marathon winner.
Jared Ward claimed the final men's spot for Rio, finishing in 2:13:00.
Amy Cragg, who finished a heartbreaking and non-qualifying fourth in the 2012 trials, won the women's race in 2:28:27.
"Looking back on it (the fourth place finish) was so good for me, it made me more determined than ever," said the 32-year-old, who made the 2012 U.S. Olympic team in the 10,000 metres and placed 11th in London.
She and training partner Shalane Flanagan dominated much of the race before the favoured Flanagan began to struggle in what officials said was the hottest marathon trials ever with temperatures in the 70s Fahrenheit.
Fellow Olympian Desiree Linden passed Flanagan in the closing mile for second in 2:29.00 to qualify.
Flanagan collapsed in Cragg's arms after finishing third and left the race in a wheelchair, but made her fourth Olympic team.
"There were times when I thought 'I'm done, I can't do this,'" Flanagan said, "But she (Cragg) talked me through it, and sweet baby Jesus I am so grateful for her."
(Reporting by Gene Cherry in Salvo, North Carolina; Editing by Larry Fine)
