Crews from Penwortham and Preston were called out to a "persons reported" fire at Meadow Brock House on Saint Ignatius Square just after 2am on October 5.
Firefighters say the fire started after cooking was left unattended in the three-storey block of flats.
The building was evacuated while crews dealt with the emergency.
A spokesman for the fire service said: "We arrived to find the two people who had been in the flat had gotten out themselves.
"It seems they'd fallen asleep after putting some food on to cook.
"The couple were checked over at the scene by paramedics."
Nobody is believed to have been seriously injured during the incident.
The cause of the fire is under investigation.