Investigators said a man entered a first-floor apartment without permission in the Park Tower complex in the 3900-block of Tower Drive around 5 a.m.
When a man inside the apartment confronted the intruder, police said the suspect stabbed him several times before fleeing the scene. The victim is expected to survive.
Richton Park police searched the area with K-9s, but were unable to locate the suspect.
Investigators are warning residents to check that their patio doors are locked.
Richton Park police continue to investigate. Anyone with information is asked to contact Detective Andrew Derewonko at 708-283-6393, ext. 436.