American record holder was considered a long shot to make the team but finished in 13min, 35.50sec.
At age 41, Bernard Lagat made his fifth and most unexpected Olympics by winning the 5,000-meter final at track trials.
The American record holder was considered a long shot to make the team, but finished in 13min, 35.50sec at the US Olympic Trials on Saturday.
Joining him in Rio will be Hassan Mead and Paul Chelimo, who nudged out a sprawling Eric Jenkins by .06 for the last spot.
Galen Rupp held the lead late but faded over the last 800 meters and finished ninth. Rupp has already qualified for the marathon and the 10,000m.
Justin Gatlin won the 200-meter final to qualify for his third Games, running the 200 in 19.75 seconds to nudge out LaShawn Merritt by .04. Also making it was Ameer Webb, who finished ahead of high-schoolers Noah Lyles and Michael Norman.
Allyson Felix made it through her semifinal and will be in the eight-woman 200m final Sunday.
The 110m hurdles title went to Devon Allen, who runs track and plays wide receiver for the Oregon Ducks. Ronnie Ash and Jeff Porter took the other spots, but left out were three Olympic veterans: David Oliver, Jason Richardson and defending champion Aries Merritt.