"Nothing Can Stop...the Sandman!" (X-362) by Lee and Ditko. 21 pages.
Flint Marko, known as the Sandman for his ability to let his body turn to sand and take any form, has been on a crime spree. The police are unable to handle him, and Spider-Man is eager to try. In their first confrontation, Spider-Man can't find a way to manage against the Sandman's various attacks. Spidey inadvertently tears his mask in the fighting and must flee or risk losing his secret identity. As Peter Parker, he has to break off a date with Liz Allen, as he is eager to start tracking the Sandman, but fate brings the Sandman to him. Marko, on the run from police, holes up in Midtown High, giving Spider-Man the opportunity for his rematch. This time, it takes ingenuity and not muscle to win the day.
First appearance and origin of Sandman (Flint Marko)
Reprinted in Marvel Collectors Item Classics #2, Marvel Tales (1966) #141, and Spider-Man Classics #5.
Collectd in Spider-Man: Doctor Octopus.