More than a decade after he won Olympic and world championship medals in freestyle swimming, Filippo Magnini is still beating other people in the water.

This time, though, he was in a race to save a drowning man who had fallen off an inflatable swan.

On Sunday, Mr. Magnini, 37, was on vacation at the Cala Sinzias beach in Sardinia, Italy, when he and others spotted a commotion in the water, Italian news outlets reported.

A man appeared to be drowning. Lifeguards climbed down from their observation tower to rush into a rescue boat. But Mr. Magnini was already ahead of them. And “with some very fast strokes,” he reached the man and kept him afloat until the lifeguards caught up, Italian news outlets reported.

“He was in great difficulty,” Mr. Magnini told the Italian newspaper Corriere della Sera.

"At a certain point he got scared, he got stuck and drank some water,” Mr. Magnini said. “When I reached him, he could not even speak.”