The 16-year-old Vietnamese prostitute in the centre of a vice syndicate, testified on Tuesday that she had lied to lawyer Spencer Gwee Hak Theng, about her age.
The court heard that she had told Gwee - who is charged with having paid sex with a minor - that she was 19 years-old when he asked for her age prior to intercourse.
Gwee, a former deputy public prosecutor, however, did not ask to see her passport, and later paid her $300 for the encounter.
The minor, who was 16 at the time of the offence, cannot be identified due to a gag order.
She was the second witness to testify at the first day of Gwee's trial.
The 60-year-old is the last of 11 men who have been charged in relation to a vice syndicate operated by a couple in Vietnam, which managed Vietnamese women flown here to work as prostitutes.
Defence lawyer Subhas Anandan, who is representing Gwee, said he would show that the investigation into his 60-year-old client was biased.
He suggested that the investigation officer of the case, Inspector Yeo Kok Leong, was "bent on charging" Gwee.
Mr Anandan also said the officer from the Specialised Crime Branch of the Criminal Investigation Department - who was the first witness to take the stand - was "very hostile to the accused" during investigations.