Their SpaceX capsule parachuted into the Pacific Ocean off the Southern California coast a day after departing the orbiting lab.
"Welcome home," SpaceX Mission Control radioed.
Splashing down were NASA's Anne McClain and Nichole Ayers, Japan's Takuya Onishi and Russia's Kirill Peskov.
They launched in March as replacements for the two NASA astronauts assigned to Starliner's botched demo.
Starliner malfunctions kept Butch Wilmore and Suni Williams at the space station for more than nine months instead of a week.
NASA ordered Boeing's new crew capsule to return empty and switched the pair to SpaceX.
They left soon after McClain and her crew arrived to take their places.
Wilmore has since retired from NASA.
Before leaving the space station on Friday, McClain made note of "some tumultuous times on Earth" with people struggling.
"We want this mission, our mission, to be a reminder of what people can do when we work together, when we explore together," she said.
McClain looked forward to "doing nothing for a couple of days" once back home in Houston.
High on her crewmates' wish list: hot showers and juicy burgers.
It was SpaceX's third Pacific splashdown with people on board, but the first for a NASA crew in 50 years.
Elon Musk's company switched capsule returns from Florida to California's coast earlier this year to reduce the risk of debris falling on populated areas.
Back-to-back private crews were the first to experience Pacific homecomings.
The last time NASA astronauts returned to the Pacific from space was during the 1975 Apollo-Soyuz mission, a détente meet-up of Americans and Soviets in orbit.
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