Detectives said the 52-year-old victim was the "intended target" of the attack in the early hours of this morning.
Officers were called to a report of a disturbance in a third-floor flat on Dumbarton Road in the Scotstoun area of Glasgow just before 1am today.
Paramedics attended but the man died at the scene.
Police Scotland appealed for information about the murder.
Detective Chief Inspector Jim Smith said: "Our inquiries are at a very early stage to establish the circumstances which led to the death of this man. Although a post-mortem examination will be carried out, we are treating his death as murder.
"At this time, it is believed that a man arrived at the flat around 0050 hours, forced his way into the house and assaulted the victim, who was not the householder. It is not clear what the motive was but it was not a random act. It would appear that the victim was the intended target, however at this time it is unclear why.
"I would appeal to anyone who was at or near the flats late on Wednesday evening into Thursday morning, and heard a disturbance or saw the suspect either arriving or leaving the scene, to get in touch.
"Anyone with information is asked to telephone police on the non-emergency number 101. Alternatively, telephone Crimestoppers on 0800 555 111 where anonymity can be maintained."
The suspect is described as a white man, 5ft 6in to 5ft 7in, medium to skinny build with short fair hair. He was wearing a light-coloured top. His age is not specified.
The area has been sealed off while forensic officers carry out a detailed examination of the scene.
Area Commander Chief Inspector Mark Sutherland said: "I would like to reassure members of the public, particularly those who live in the area of the flats, that everything is being done to trace the person responsible.
"I am aware that local residents will be shocked and alarmed by this incident, however extra patrols will be in the area and I would urge anyone who has concerns to speak to the officers."