Paolo Lorenzi booked his spot in round two of the Kremlin Cup after fellow Italian Filippo Volandri retired from their clash in Moscow.
Volandri dominated the first set but his compatriot had moved 4-6 7-5 4-1 ahead by the time the world No 91 pulled out due to a hip injury.
Lorenzi's victory sets up a second-round encounter with Andreas Seppi, another Italian who is seeded second at the Russian tournament.
"It was a very tough and close match. He (Volandri) had a match point so I was lucky I managed to survive," Lorenzi said.
"It wasn't easy to play against him because we are very good friends. This morning we warmed up together. It's not easy when you know each other so well."
Elsewhere on Tuesday, Kazakhstan's Mikhail Kukushkin defeated home hope Alex Bogomolov Jr 6-4 6-1. Kukushkin's compatriot Andrey Golubev beat Ukraine's Oleksandr Nedovyesov 6-2 7-5.
There was better news for the home crowd as Evgeny Donskoy battled past Marcos Baghdatis 6-3 3-6 6-4.