The 104th City to City Marathon, one of South Africa's oldest premier long-distance events, takes place from Pretoria to Johannesburg on September 23.
Central Gauteng Athletics' general manager, Mandla Radebe, said: "The plan is to make it bigger and better. Entries go out throughout the country from tomorrow.
"One big company which promised to sponsor us has since withdrawn. But we are delighted the City of Johannesburg and the City of Tshwane have come on board, which is a major boost for us.
"It would be great to have in the region of 5000 runners participating, but we had some internal challenges around sponsors.
"Those challenges also resulted in the marathon being postponed from September 2 to 23, but we are on track to deliver a great event," Radebe said.
Some of the top runners expected to participate in the marathon include Fusi Nhlapo, Andrew Kelehe, Sarah Mahlangu and Pauline Phaho.
As usual, runners from neighbouring Zimbabwe are expected to challenge for the honours, especially in the senior men's and women's categories. Other countries whose runners usually take part in this event include Lesotho, Swaziland and Namibia.
"The majority of top runners use the event as part of their early preparations for the Two Oceans and Comrades marathons," Radebe said.
The marathon starts at 6am at Hennop's Park in Centurion and finishes at Hans Schoeman Street in Randburg.
A 20km road race and walk starts in Woodmead.