The Romanian withdrew from the Brisbane International last week because of the injury, which also affected her 2015 campaign, and she called the trainer during her second-round match.
Halep, who was given a first-round bye, said the pain was coming and going but she produced some of her best tennis in the deciding set on the way to a 6-4 2-6 6-1 victory that set up a quarter-final against Czech fifth seed Karolina Pliskova.
"When you have pain you always get scared because you don't know what is going to happen," she said after her win.
"I felt actually yesterday during the practise same thing. Five minutes pain, five minutes without pain.
"I don't know exactly what this is. MRI showed that I have just an inflammation and I can keep playing, so I will do my best and I will try to be there, to stay focussed."
The 24-year-old is one of four leading women players heading to the Australian Open, which begins in Melbourne on Monday, under an injury cloud.
World number one Serena Williams (knee), fifth-ranked Maria Sharapova (arm) and number three Garbine Muguruza (foot) all withdrew from matches in the last week.
Halep said before the clash with the 34th-ranked Garcia she was fit but she looked anything but during her medical time out after the Frenchwoman stepped up the aggression to take the second set.
Halep, though, shrugged off the complaint to storm through the third set, reeling off five straight games and recording her first win of the year when Garcia netted a straightforward mid-court forehand.
"I needed matches to see if I can stay during the match until the end with my achilles," she said.
"I did well today. I'm happy that I could finish. I am happier that in the third set I didn't feel the pain. It means that I can keep working and keep playing with tough opponents."
(Writing by Patrick Johnston in Singapore and Sudipto Ganguly in Mumbai, editing by Ed Osmond)
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