The long-awaited moment of contact came as two of the crew were winding up a spacewalk.
Spacewalkers Michael Fossum and Ronald Garan Junior took care of all the preliminaries, removing covers and disconnecting cables on the bus-size lab, named Kibo - Japanese for hope.
They left it to their colleagues inside to do the heavy lifting, by way of the space station's robot arm.
The honour of operating the arm for the installation fell to Japanese astronaut Akihiko Hoshide, who accompanied Kibo to orbit aboard space shuttle Discovery.
"We have a new hope on the international space station," announced Mr Hoshide.
"Fantastic job," Mission Control replied.
Kibo -- a behemoth stretching 37 feet and weighing more than 32,000lbs -- became the largest lab at the space station by nine feet.
It is also more sophisticated. Kibo sports a hatch to the outside and a robot arm for sliding out science experiments. A smaller arm will arrive next spring, along with an outdoor porch for holding the experiment packages.