Transforming the old club into a world-class training environment was an initiative of council-owned company Bay Venues.
Chief executive Gary Dawson said it had only been 12 months since the council decided to back the proposal.
"It happened within a year, and that is remarkable. We took a building that was becoming derelict and a liability and turned it into a fantastic asset for the city and the country for a relatively small investment."
A lot of structural work was needed to make it watertight which ended up costing the council an extra $150,000 on top of its original budget of $977,000.
The council's share of the project was to "make good" the old building by bringing it up to modern seismic standards, together with re-roofing and weather tightness works.
Bay Venues raised the rest of the $3.5 million needed to create the sport centre that will be home to the New Zealand Rugby Union's men's and women's sevens teams and the offices of the Bay of Plenty Rugby Union.
"You wouldn't know it used to be the Cossie Club ... all credit to the council for backing us, and everybody else," he said.
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Centre manager Justine Brennan said she was working with the University of Waikato on confirming its tenancy which will include a laboratory and state-of-the-art environmental chamber. Other tenants included Body In Motion Physiotherapy and Sports Medicine.
She said the location of the centre next to Blake Park and its proximity to the beaches, Mauao and the Mount Hot Pools was a huge bonus.
"We have it all in the one place at the Mount."
Mr Dawson said the centre was budgeted to run at a small surplus in the first year of operation. This included the costs of depreciation and debt servicing.
The budget did not include potential revenue from casual use by sports teams, like regional squads gearing up for tournaments by going through testing and video analysis.
The centre included a special video analysis room.
Another feature of the centre was hot and cold plunge pools and an upstairs athletes lounge and kitchen.
Mr Dawson said they were not competing with private gyms because it was not available for use by the general public. "It is a high performance centre."
Interest was being shown by many other codes including AFL, netball, cricket, surf life saving and soccer.
Mayor Stuart Crosby said the project would further enhance Tauranga as a destination for world champions and athletes wanting to grow their careers.