"There’s nothing wrong with the deal, that’s why we signed. It’s only when it came to implementation that we ran into problems," he told thousands of supporters at a rally in Zimbabwe’s second city Bulawayo and opposition stronghold.
The power-sharing deal is seen as Zimbabwe’s best hope for rescuing an economy where fuel and food are scarce and inflation stands at 231 million percent, the world’s highest.
Heads of state who form regional grouping SADC’s defence and security committee are due to meet in Swaziland on Monday for talks to try to secure a breakthrough.
Mugabe, Tsvangirai and Arthur Mutambara, leader of the smaller MDC faction, will take part in the troika meeting of the leaders of Angola, Mozambique and Swaziland, Mbeki has said.
"We agreed to go to SADC, so we’re going on Monday. We want this marriage to work. If we agree to everyone’s satisfaction, we will return and form a government," said Tsvangirai, who also described the negotiations as the "dialogue of the dead."
"It’s a one-man monologue. Mugabe doesn’t negotiate, he just says ‘No. I don’t want’," he said.
Tsvangirai beat Mugabe in a March 29 presidential election but fell short of enough votes to avoid a June run-off, which was won by Mugabe unopposed after Tsvangirai pulled out, citing violence and intimidation against his supporters.
Mugabe’s victory in the run-off was condemned around the world and drew toughened sanctions from Western countries whose support is vital for reviving Zimbabwe’s ruined economy.
Tsvangirai suggested a new leadership would find it hard to work together given years of animosity between him and Mugabe.
"When we return from Mbabane and if we get to form the government we will, from the start, have a problem of trust," said Tsvangirai.
Tsvangirai threatened to pull out of talks last Sunday after Mugabe allocated powerful ministries such as defence, finance and home affairs to his own party.
Mbeki said on Friday a deal was still possible despite another round of inconclusive talks. But his role has been thrown into doubt since South Africa’s ruling ANC party forced him to resign.