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.
If found guilty, Anwar could be jailed for 20 years, in effect ending his political career.
The 62-year-old Anwar has repeatedly denounced the trial, saying the charges had been trumped up by political opponents looking 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, the prime minister, and the premier's wife Rosmah Mansor, 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 25-year-old accuser.
He added that his defence team planned to call the prime minister and his wife as witnesses.
Najib, who was deputy prime minister at the time, has acknowledged Saiful visited him but says it was in connection with a university scholarship.
The government has denied any interference and has promised that Anwar will receive a fair trial.
The trial had been scheduled to start in July but was repeatedly delayed due to appeals by Anwar's lawyers.
It was delayed again on Tuesday by several hours after Anwar's lawyers sought a date to review a higher court ruling, which refused to allow the defence team access to certain prosecution evidence.
Al Jazeera's Veronica Pedrosa, reporting from outside the court in the capital, said the case has also placed the judiciary on trial.
A lot was at stake, she said, as evidenced by the presence of many opposition figures chanting their support for Anwar at the court and a minor scuffle with police who were trying to bring them under control.
|Amnesty International criticised the trial, calling it "politically motivated" [Reuters]
Rights group Amnesty International has urged the Malaysian authorities to drop the charges against Anwar, calling them "politically motivated".
"The Malaysian authorities have resorted to the same old dirty tricks in an attempt to remove the opposition leader from politics," Sam Zarifi, Amnesty's Asia-Pacific director, said last week.
"Anwar’s case has rightly raised doubts among the international community and investors about Malaysia’s commitment to justice and the rule of law," he said, adding: "Malaysia’s judiciary should throw out these charges."
Anwar, a married father of six, was sacked as deputy prime minister and finance minister in 1998 amid a policy row and political feud with Mahathir Mohamad, the then prime minister.
He was convicted of corruption and sodomy in a trial that drew international condemnation, and spent six years in prison before being freed in 2004.
Malaysia's highest court later overturned the conviction for sodomy but doubts remain whether Anwar, who represents the biggest political threat to the ruling party that has governed Malaysia for 52 years, will get a fair trial this time.
Anwar led a three-party opposition alliance to unprecedented gains in the 2008 general elections, denying the ruling coalition a two-thirds parliamentary majority for the first time in 40 years.