When bystanders alerted him to an accident near his clinic in Bukit Batok Central, Dr Stanley Peck, 48, rushed out with an emergency kit and performed chest compression on the girl, who was unconscious.
Meanwhile, nurses from another clinic attended to her with an oxygen mask and an intravenous drip.
Unfortunately, Eleanor Tan, four, died in the accident involving a car on Monday. A police spokesman said the 53-year-old male driver was arrested for causing death by a rash act.
A 37-year-old woman believed to be the girl's maid was also hit in the accident, which happened at about 6.40pm.
Dr Peck, who works at Lighthouse Clinic and Surgery at Block 642, Bukit Batok Central, said the girl was bleeding from the head and there were bruises on her legs. He added: "She didn't have a pulse."
The doctor and the nurses attended to the girl for about 10 minutes before the ambulance arrived.
Barber Low Ko Chim was sitting outside his shop at Block 644, Bukit Batok Central, when he heard a crash.
"I saw the woman and the girl lying on the road a few metres apart," said the 63-year-old.
"I went down to see if I could help because I know some first aid from when I was in the St John Ambulance Brigade."
He kept the woman conscious by talking to her, while waiting for the ambulance. He was later joined by a doctor, who stopped to offer assistance while passing by in a taxi.
The police were alerted at 6.41pm to the accident, which happened in the direction of Bukit Batok West Avenue 2. The Singapore Civil Defence Force (SCDF) said it sent two ambulances. Eleanor and the woman were taken to Ng Teng Fong General Hospital.
Shin Min Daily News reported that the girl's mother, Ms Jacelyn Wong, 24, was at home preparing her daughter's favourite meal of steamed eggs.
"All mothers have a sixth sense; I felt disturbed when I was cooking," Ms Wong told Shin Min Daily News.
She waited at home until 8pm, thinking that Eleanor was late because of a train disruption. "When I received the call from the hospital, I thought that my daughter had only been injured. But when I got to the hospital with my husband, we found out she had died," she said.
Attempts by The Straits Times to contact Ms Wong were unsuccessful.
Mr Low said people often cross the busy road at that point, even though there is an overhead pedestrian bridge nearby.
Ms Wong wrote on her Facebook page early yesterday morning that though "our precious daughter Eleanor Si Xuan has left us, she will always be in our hearts... I sincerely thank each and every one of you who dote on our precious angel".
• Additional reporting by Zhaki Abdullah and Fabian Koh