Saeid Abdevali had already snatched a bronze medal in the 75kg weight category.
In the 98kg, gold medallist at the London 2012 Olympics, trailed Sweden's Fredrik Schoen 4-0 at the end of the first period, but when the wrestlers went into par terre in the second period, Rezaei was able to turn Schoen twice to tie the match and take the advantage on criteria.
The score held up, giving the Iranian his second Olympic medal.
Cenk Ildem of Turkey earned another bronze medal in the division, taking down Alin Alexuc Ciurariu of Romania.
"I believe that it was a technical mistake that I made during the match, but I was able to recover very quickly," Rezaei said afterward. "It was from previous experience knowing that in the Olympics one move could make a difference. I wanted to make sure I could come back and I did."
Artur Aleksanyan of Armenia defeated Cuban Yasmany Daniel Lugo Cabrera to win the gold medal.