Anwar has been charged with consensual sodomy but his former aide, Saiful Bukhari Azlan, insisted under cross-examination by the defense on Tuesday that he was sodomised against his will.
The former deputy prime minister denies the charge, which he says is politically motivated to prevent him from wresting power following the government's record losses in the last general election in 2008.
A conviction in the trial, set to end in late August, carries a maximum 20-year jail term, one which would end the career of the 63-year-old politician.
Sex between males is illegal in this conservative Southeast Asian country. Consensual and non-consensual sodomy are listed as separate offenses.
The prosecution argued it was entitled to charge Anwar for either consensual or non-consensual sodomy but Anwar's lawyer, Karpal Singh, later told reporters he would move to have Saiful disqualified for contradicting the charge.
"This is the first time in a criminal case in this country that you have a statement to the police saying that the act was non-consensual and yet the charge says consensual," Anwar told reporters outside the packed courtroom.
Malaysian media have lapped up lurid details of the politically charged trial and have published photos showing "in camera" trial proceedings that prompted complaints by the opposition of bias.
Analysts say the sensational media coverage signals a more important battle over the case that is being waged in the court of public opinion between the Anwar-led opposition and Prime Minister Najib Razak's ruling coalition.
"Despite the proceedings, in the court of public opinion people already seem to have made up their minds," said political analyst Ong Kian Ming.
"The more important question now is how far the continuing revelations in the trial will affect Anwar's image among those who now feel that this charge was manufactured," said Ong.
Anwar leads an opposition group that denied the ruling coalition control in five of Malaysia's 13 states but was hit by a series of recent setbacks, including the resignation of four opposition MPs.
Victory by the ruling National Front of Prime Minister Najib Razak in its first parliamentary by-election since the 2008 general election has boosted the government's confidence.
But analysts say the country's non-Muslim minorities who abandoned the government due to alienation have yet to swing back to them. Tensions have also gone up due to a row over the use of the word "Allah" by Christians to describe God.
Najib took office in April 2009 pledging political and economic reforms to revive his ailing coalition and win back foreign investment.
But the uncertainties have helped dent foreign investment. Net portfolio and direct investment outflows reached $61 billion in 2008 and 2009, according to official data.
Flows have returned to the Malaysian bond market, with official data showing foreign ownership of Malaysian government bonds rose to 55.4 billion Malaysian ringgit ($17.32 billion) as of March 10 from 41 billion ringgit, largely after a central bank rate hike and speculation of a Chinese currency revaluation.
