The Western Bulldogs had kicked the opening three goals of their AFL match in the first five minutes.
Nash had started on the interchange bench and knew things had to change fast.
He earned praise from coach Sam Mitchell for helping spark the Hawks' quick rebound, which gave them the lead by late in the first quarter.
They were in front for most of the game, rallying again in the final term when the Bulldogs briefly hit the front and winning by seven points.
"He says 'we need to change this game, we're in control here, we need to change the narrative'," coach Sam Mitchell said of Nash's early influence in the game.
"When you have players who are willing to make a change in a game, that's what we really need. We've been working enormously hard on that and there was some reward for effort.
"We handled some momentum swings well...we've been a bit hit-and-miss with that."
It is Hawthorn's second win for the season and a massive confidence boost, especially given Sydney had mauled them the week before.
"The character the boys showed was fantastic. Their belief and commitment in what we had done, through the week, through the month, through the year, through the years - you're always looking for evidence you're on the right track," Mitchell said.
The Hawks were led superbly by captain James Sicily, who stayed in the game despite a dislocated shoulder in the first term and an ankle injury in the third.
He went forward in the last quarter and kicked a crucial goal.
Mitchell said post-game he has no idea whether Sicily will be ready for Saturday's Launceston game against St Kilda.
The Hawks coach also praised defender Jarman Impey and utility Blake Hardwick for their strong games, while Calsher Dear kicked two goals on debut.
Dear is the son of Hawks premiership ruckman Paul Dear, who died two years ago of cancer. Mum Cherie flew back from a holiday in Europe to watch her son's AFL debut.
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