The crew quickly located and sealed the tiny hole that created a slight loss of pressure, and space officials said the station has remained safe to operate.
Russian cosmonauts were to carry out a spacewalk Tuesday to examine a mystery hole in a Soyuz spacecraft docked on the International Space Station that a Moscow official suggested could have been deliberate sabotage.
What makes it especially hard is that the Soyuz spacecraft, unlike the ISS, was not created to be repaired in spacewalks and has no outside railings for astronauts to hold onto. The fix halted the leak, and the space station has since maintained a steady pressure. As they cut into the spacecraft, small fragments of the material floated away and formed a cloud of debris.
The spacewalk was the fourth for Kononenko and the second for Prokopyev.
You need steady hands when you're hurtling around the Earth at 27,000 kilometres per hour in a pressurised spacesuit holding a knife and hacking a hole in a Soyuz capsule from the outside.
The hole appeared as a black mark or spot on the exposed metal skin of the Soyuz spacecraft. The damage was apparently patched before the Soyuz actually launched into space, and it wasn't until it was attached to the space station that the makeshift repairs broke loose and started leaking.
Kononenko used a pair of forceps and a swab to collect samples of the dark epoxy.
Samples taken by the two cosmonauts will eventually be returned to Earth for investigations to be completed to find the possible cause of the hole. This part of the capsule will be jettisoned as usual before atmospheric re-entry, and so poses no risk for descent.
Tuesday's spacewalk began at 10:59 a.m. EST (1559 GMT) and ended at 6:44 p.m. EST (2344 GMT) when the hatch to the Pirs docking compartment was closed. Then the insulation proved harder to remove than expected, taking another one to two hours of effort. It was the first-ever operation to unseal the meteorite protection shield during a spacewalk in the history of space exploration.
Prokopyev, who's been on the station for six and half months, will use the MS-09 he's investigating Tuesday to return to Earth with the European Space Agency's Alexander Gerst and NASA's Serena Aunon-Chancellor on December 20.
Nasa said it was a "Eureka Moment", as the hole was found after several hours.