The big victory came two days after Gay ran a world-leading 9.75 seconds to win the 100 metres at the U.S. meeting in Des Moines, Iowa.
"It feels good to do that," said the 2007 triple world champion who has been beset by numerous injuries since then. "I am just happy to be healthy."
Collegian Isiah Young took second place in the 200 at 19.86 with Curtis Mitchell third at 19.99.
The win assured Bolt and Gay, barring injury, will both be in the 100 and 200 metres at the August 10-18 championships in Moscow.
Bolt won the 100 at the Jamaican championships in Kingston this weekend and has a wild card bye in the 200 metres.
Both also will run the 4x100 metres relay for their nations in Moscow.
Jamaican sprinters have dominated the Americans in the past two Olympics and world championships.
Gay, who displaced Bolt as the year's fastest 200 metres runner, would not be drawn into a war of words over whether the U.S. sprinters were ready to end Jamaica's streak.
"It's no secret Usain Bolt is obviously the greatest of all time," Gay said. "He's definitely going to be prepared."
Gay's triumph overshadowed losses by Olympic champions Aries Merritt and Allyson Felix on the final day of the U.S. trials.
World 110 metres hurdle record holder Merritt, coming back from a hamstring injury, finished third behind Ryan Wilson and David Oliver but still made the U.S. team.
Wilson ran 13.08 followed by Oliver at 13.11 and Merritt in 13.23, with only the top three finishers in each event qualifying for the worlds.
"I had to fight because I knew I had to make the team," said Merritt, who had only two workouts before the nationals.
Collegiate champion Kimberlyn Duncan upset Felix in the women's 200, winning in a wind-assisted 21.80 seconds to Felix's 21.85. Jeneba Tarmoh took third.
Olympian Duane Solomon took the men's 800 metres final in a world-leading one minute 43.27 seconds, and London Olympics gold medallist Jenn Suhr dominated the women's pole vault, clearing 4.70 metres (15 feet, 5 inches).
- Sports & Recreation
- Athletics, Track & Field
- Usain Bolt
- Allyson Felix