Key forward Koschitzke was desperate to prove his fitness for a one final match, his 200th, before retiring.
Koschitzke hadn't played since round 14.
Midfielder Montagna says he made the switch with the ageing warhorse Koschitzke during a warm-up lap at the start of the training session.
"They were still umming and ahhing about whether to play him and he needed to make sure he ticked certain boxes," Montagna told The Footy Show on Thursday night.
"He had spent about six or eight weeks trying to get himself up.
"We just decided in the warm-up lap, I said, 'Kosi, give me your GPS and get the kilometres up'... It got him a game. It all worked out in the end."
Koschitzke came off the bench in the second half as the substitute player for the last-round clash with Fremantle and the Saints enjoyed a 71-point win at Etihad Stadium.
