The province is in negotiations with a developer to sell a parcel of land at 11 Wellesley St. W.
But Wong-Tam has approval to use city money to try to negotiate to keep about half a hectare of the land for green space.
"This is the very last opportunity to build a park of this significant size, in a very dense urban environment," she said.
She had hoped the province would sell the land back to the city but Ontario is now reviewing bids from developers.
Wong-Tam says Toronto has to save green spaces because they are disappearing as condo towers multiply.
"Just because one is a downtown resident doesn't mean we all chose to live in concrete jungles," said Wong-Tam.
Paul Farralley of the Church Wellesley Neighbourhood Association has been fighting to stop what he says is out-of-control condo development.
"Developers are coming in with massive condos that belong on Bay Street. It's just the level of intensification that's going on," he said.
Wong-Tam still needs full council support to try and save the green space.
The property is estimated to be worth between $65 and $70 million.