The woman suffered burns to her face, arms and chest and was listed in critical but stable condition, said Capt. Roger Mora of the Montclair Fire Department.
Her 74-year-old partner, who ran back inside the burning home to try to save her, was also taken to the hospital with smoke inhalation and other medical issues, authorities said.
Authorities were alerted to the fire around 12:30 a.m. Saturday, Mora said. When they arrived, firefighters could see black smoke and flames coming from the home in the 5500 block of Granada Street.
The man was found near the front door of the home and was struggling to breathe, Mora said. The man managed to tell rescuers the woman was still in a rear bedroom.
Firefighters found the woman and pulled her to safety, Mora said. Paramedics took her to Arrowhead Regional Medical Center in Colton.
The home sustained about $50,000 in damage, Mora said.
The home reportedly was equipped with working smoke detectors and a home security system.
It was unclear what caused the blaze and where it originated.
While it's unclear if Saturday's fire was ignited by a space heater, Mora advises residents to make sure to keep all items away from heat sources, including space heaters, to prevent fires.
He also suggested people keep fresh batteries in their smoke detectors.
Reach Beatriz via email, call her at 909-386-3921, or find her on Twitter @IEBeatriz.