The three-man crew blasted off right on schedule from the once-super-secret Baikonur cosmodrome, prompting Americans to burst into applause and Russians to start pouring the cognac.
"It is huge -- it is testament to our partnership and how deep it really is," said Sean O'Keefe, head of NASA, as he overlooked the launchpad deep within the unwelcoming Kazakh steppe.
The launch came three days after China became the world's third space-faring nation, joining the ranks of the Soviet Union - now Russia - and the United States.
But while the Chinese launch was seen as a vehicle of national pride, Russia -- which pioneered space travel more than four decades ago - portrayed Saturday's flight as a demonstration of international unity and cooperation.
The Soyuz spacecraft is taking the next U.S.-Russian replacement crew to the $60 billion space station, and giving a European Space Agency astronaut a ride into space.
"Our Russian partners stepped up at a time when we needed them the most. They are shouldering a particularly heavy burden and we are grateful for that," O'Keefe said.
The launch is the second since the U.S. space shuttle Columbia disintegrated in February, causing NASA to put a hold on flights.
Since the Columbia accident, NASA has depended on Russia to keep its astronaut corps flying. The Russian Soyuz, whose primary role had been to serve as an emergency evacuation craft for the station, is now the only ship capable of carrying crews to and from the 16-nation space outpost.
"We are happy to have the opportunity to help our partners in the space station," said Sergei Gorbunov, spokesman for the Russian Space Agency, Rosaviakosmos.
U.S. astronaut Michael Foale, making his sixth trip into space, is commander of the flight, which also includes Spaniard Pedro Duque and flight engineer Alexander Kaleri.
The crew blasted off under clear blue skies, shooting across the barren Kazakh steppe at the start of their two-day trip to the space station. Docking is scheduled for Monday.
Foale will become the only American to have served aboard both the Mir space station and the International Space Station. Foale and Kaleri are due to replace American Ed Lu and Russian Yuri Malenchenko, who have been in space since May.
Malenchenko, who left the planet a signle man, will return to a wife, after getting married aboard the space station in a ceremony that caused a stir.
Duque, who will carry out a series of experiments in space, will return with Lu and Malenchenko in another Soyuz capsule in ten days.
"It was just so beautiful," said Foale's wife Rhonda, who clutched a Union Jack flag in recognition of her husband's British birthland. "It felt good and I'm glad he's having a good time up there."
The new space station responsibilities have put a strain on the Russian space program's budget, but have also boosted the prestige of an agency that was derided a few years ago for becoming a provider of expensive junkets for rich space tourists.
Jean Jacques Dordain, the director the European Space Agency, praised the Russians for providing a path to space for other astronauts.
Russian launches are steeped in history and tradition. On Saturday, as the rocket roared into the sky trailing a tail of fire, the crowded grandstand applauded then grew immediately silent. Every 10 seconds, controllers issued reports, declaring that everything was proceeding normally.
Almost 10 minutes after launch, the Russian space agency announced that the crew had reached orbit, causing the grandstand to burst into applause. Duque's mother, Andrea, sat quietly, clutching a cane, tears shining in her eyes.
"There are a lot of traditions involved," said Norm Thagard, the first American to fly to space onboard the compact Russia Soyuz in 1998. Visiting Baikonur for the first time since his trip, Thagard said much looked the same.
The Russians say that's natural.
"When you've been doing it for four decades, if something works, you don't change it," said Vladimir Popov, who heads the Russian space unit responsible for all rescue and search missions.