Smeltz kept his nerve on 79 minutes to settle the game from the spot.
Earlier, the Kiwi struck a long range wonder goal to put the Queenslanders 1-0 ahead at halftime.
Sergio van Dijk from the spot and Matthew Leckie had Adelaide 2-1 ahead before Bruce Djite, the former Reds striker, tapped in to bring Gold Coast level.
The winning goal came after Joel Porter was pulled down inside the Adelaide area.
Smeltz initially made no mistake from the spot, but was forced to re-take the shot after Djite infringed before the penalty was taken.
However, it mattered little to the Kiwi, who settled the issue at the second effort.