The deadlock has stalled the formation of a unity government which would see Mugabe remain as president and his rival become the prime minister.
The talks come amid mounting international pressure for a solution to the crisis in Zimbabwe.
On Monday the European Union tightened sanctions on the country by adding more than 60 pro-Mugabe officials and companies to a visa and assets freeze that bans them from travelling to or trading with EU nations.
The blacklist which now totals 203 people and 40 entities is aimed at increasing pressure on Mugabe to stand down.
Announcing the new measures EU officials said most if not all of the 40 entities on the blacklist were fake companies used to funnel money to prop up Mugabe's government and supporters.
Western governments have repeatedly called for Mugabe to resign and are also pushing for major economic reforms before aid is offered.
The Pretoria talks hosted by Kgalema Motlanthe, the South African president, comes a week after power-sharing talks in Harare between Mugabe and Tsvangirai collapsed.
Bright Matonga, the country's deputy information minister, has said Mugabe would form a government after the summit with or without a deal with Tsvangirai.
Tsvangirai has accused the Mugabe's ruling Zanu-PF party of trying to sideline his Movement for Democratic Change (MDC), adding that no deal is possible unless detained party activists are freed.
Al Jazeera's Haru Mutara, reporting from Harare, says many Zimbabweans have given up hope that the meetings could end the political deadlock.