Peter Rowe said he and two friends had just finished racing up the staircase at the city's Museum of Art on Saturday when they saw Sylvester Stallone.
"He said to us 'Man, you guys are fast. You're making me look bad!'" Rowe said Tuesday.
Stallone then posed for a selfie with the trio, putting up one fist.
"Look tough, guys!" he said, according to Rowe.
Stallone made the steps famous in his first turn as fictional boxer Rocky Balboa, who used them as part of his training regimen. Thousands of people now visit the steps each year to recreate the run and to take pictures with a Rocky statue, which was originally a prop in "Rocky III."
Rowe's friends, Jacob Kerstan and Andrew Wright, were visiting him from Azusa Pacific University in greater Los Angeles. Rowe, 22, recently graduated from the school and moved to the Lancaster area, about 60 miles west of Philadelphia.
Yet in all the time spent in L.A., Rowe said, they never saw a famous person.
"What are the chances of meeting him, that celebrity, right there?" he said, calling it "an unreal experience."
Stallone is in Philadelphia for the shooting of "Creed," the latest installment in the series. It stars Michael B. Jordan ("Fruitvale Station") as the grandson of early Rocky foe Apollo Creed.
Fans Meet Stallone At Rocky Steps
Three fans of the movie "Rocky" had a chance encounter with Sylvester Stallone after running up the steps of Philadelphia's Museum of Art.