Specialist teams of officers were trying to trace the movements of a man who attacked a young woman in Govanhill.
Footage from CCTV cameras across the South Side is being examined in a bid to find out more about the attack.
As reported in late editions of last night's Evening Times, the 24-year-old was subjected to the terrifying ordeal in Dixon Avenue, in the early hours of Monday morning.
Forensic officers in white protective suits could be seen carrying out investigations outside a close in street.
A massive police operation was launched early yesterday after the victim reported the incident.
Several roads around the crime scene - including Dixon Avenue and Cathcart Road - were closed off for much of yesterday as police carried out investigations.
Uniformed officers stood guard at a police cordon as detectives did the rounds.
The attack came just a week after city police launched a hunt for three men who gang raped a woman.
That attack also took place in Glasgow's South Side - around a mile from Govanhill.
Officers are not linking the two incidents.
There is currently no description of the suspect available.
A spokeswoman said: "We can confirm Police Scotland detectives are investigating a report of a serious sexual assault in the area of Dixon Avenue, Glasgow in the early hours of Monday.
"Extensive inquiries are ongoing."
Police are still appealing for witnesses after three men raped a woman in Toryglen.
The 33-year-old was dragged into a close and attacked in Edinbeg Avenue, between midnight and 3am last Saturday.
Anyone with any information is asked to call Police Scotland on 101.