The Soyuz blasted off from Russia's Baikonur cosmodrome in Kazakhstan on Thursday after two postponements while technicians fixed a mechanical glitch that affected the craft's ability to attach itself to the orbital platform.
"The Soyuz has docked well with the International Space Station," an official announced at mission control in Korolyov, just outside Moscow on Saturday.
But in a rare occurrence, the astronauts had to dock manually instead of automatically as the Soyuz was approaching the ISS too quickly.
"The docking today looked excellent. I was observing the transition from automatic to manual and it appeared seamless," said Fred Gregory, deputy head of the US space agency Nasa.
"The crew was extremely well-trained - there was no excitement; it appeared extremely routine."
Three hours later, Russian cosmonaut Salizhan Sharipov and American Leroy Chiao floated through from the Soyuz into the
Russian cosmonaut Gennady Padalka, in orbit since April, opened the hatch to the newcomers and he and US astronaut Michael Fincke greeted Sharipov and Chiao with smiles, hugs and kisses.
Sharipov and Chiao will take over from Fincke and Padalka for the next six months.
Russia has been a lifeline to the
station since Columbia crashed
"It was very worrying but everything went well, thank God," said Nigara, Sharipov's 16-year-old daughter, watching at mission control with the rest of the family.
"He has never been away for such a long time before - but he will ring us every day on a satellite phone and he will be able to email us."
A third crew-member, Russian space forces officer Yuri Shargin, is on a 10-day mission and is due to return to Earth with the outgoing crew at 0030 GMT on 24 October.
Russia has been the sole lifeline to the station since February, 2003, when the United States grounded its shuttle fleet after Columbia disintegrated on re-entry, killing the seven-person crew.
US shuttle flights to the station could resume in May, officials have said, but in the meantime Russia will continue to launch all manned and cargo ships.