Robinson said the pieces, which serve as filler between the heat-resistant tiles, came out easily during the six-hour spacewalk. "It looks like this big patient is cured," he said, Reuters reported.
He did not have to use a makeshift hacksaw put together in orbit that he brought along just in case.
NASA officials had determined that the exposed ceramic-fiber fillers could lead to overheating and a possible repeat of Columbia's disintegration during re-entry in 2003.
Discovery is docked at the International Space Station on the first shuttle mission since the Columbia disaster.
With fellow spacewalker Soichi Noguchi watching from a perch on the ISS, Robinson attached a special foot restraint to the space station's 58-foot robotic arm and fellow astronauts maneuvered the arm so he could get a look under the shuttle.
The astronauts took care not to have his feet or helmet touch the orbiter's fragile tiles.
Once under Discovery's belly, Robinson planned to spend about an hour trimming or removing the filler strips near the shuttle's nose, but it took him only seconds for him to pull each strip.
There are 24,300 glass-coated tiles on the shuttle, most on its belly, according to the Associated Press. The tiles protect the shuttle from extreme temperatures during orbit, and more importantly, during launch and re-entry.
The filler keeps the tiles from bumping against each other during launch but isn't needed during re-entry because of a difference in airflow.
NASA officials said Tuesday they are considering another spacewalk Friday to fix a protrusion in an insulating blanket outside the shuttle commander's window, according to Reuters.
Before Wednesday's landmark repair job, Robinson and Noguchi attached an external storage platform to the $95 billion space station.