
China’s world champion Tang Qianting took the silver medal and Ireland’s Mona McSharry shed tears of joy and amazement after an extraordinary three-way battle for bronze.
Tang led at the turn but Smith, only fourth at that point, powered back to win in one minute 05.28 seconds, 0.26 seconds clear of the Chinese, to make up for securing silver in the event in Tokyo.
The winning time was slower than the 1 minute 5.00 seconds Smith had clocked in the heats.
McSharry touched out third by the very slimmest of margins, beating Italy’s Benedetta Pilato and world record holder and 2016 champion Lilly King of the US both by 0.01 of a second.
The 23-year-old’s medal was Ireland’s first of the Games and there were plenty of her supporters in the stands.