"The prosecution will then prove [guilt] beyond reasonable doubt through the testimony of Mohamad Saiful Bukhari Azlan and forensic evidence from doctors and chemists alongside circumstantial evidence and documentary evidence," Mohamed Yusof Zainal Abiden, the deputy public prosecutor said.
Sodomy, even among consenting adults, carries a penalty of up to 20 years in Malaysia.
The trial began on Tuesday after months of delays caused by defence applications to strike down the case and obtain access to evidence including medical reports and closed-circuit television footage, denied them by a higher court ruling.
The case has placed the Malaysian judiciary under scrutiny again after Anwar's conviction for the same offence almost a decade ago was eventually overturned.
The 62-year-old Anwar has repeatedly denounced the allegations against him, saying the charges are an attempt to end his challenge to the government.
Speaking to reporters outside the court on Tuesday, Anwar blamed "the machinations of the dirty, corrupt few" and accused Najib Abdul Razak, Malaysia's prime minister, and Rosmah Mansor, the premier's wife, of being responsible for the trial.
Anwar said that both Najib and his wife had met his accuser and had interfered with the legal process.
"They were personally involved in this conspiracy and frame-up. We have evidence that Saiful Bukhari was in the house with Rosmah and met Najib a few days before he lodged the police report," Anwar said, referring to his accuser.
He added that his defence team planned to call the prime minister and his wife as witnesses.
Najib has acknowledged Saiful visited him, but says it was in connection with a university scholarship.
Anwar, a married father of six, has faced such charges before.
In 1998, after he was sacked as deputy prime minister and finance minister amid a policy row with Mahathir Mohamad, the then prime minister, and was charged with corruption and sodomy.
The trial drew international condemnation, but Anwar was convicted and spent six years in prison before being freed in 2004 when Malaysia's highest court overturned the sodomy conviction.
In 2008, Anwar led a three-party opposition alliance to unprecedented gains in Malaysia's general elections, denying the ruling coalition a two-thirds parliamentary majority for the first time in 40 years.
The government has denied any interference and has promised that Anwar will receive a fair trial.