British swimmer Andrew Lindsay had to work hard over the final stages of his race to successfully defend his S7 100m backstroke Paralympic title.
The 24-year-old Scot clocked one minute 16.37 seconds to beat Argentina's Guillermo Marro by just 0.31 seconds, with team-mate David Roberts fourth.
"I had to really dig deep over those last 25 metres," said Lindsay.
"I could see Marro closing in over the final stages. It was a shock as I'm not used to him being that close to me."
Lindsay had set a new Paralympic record of 1:15.49 in the morning heats and said his time in the final was 'shocking'.
"I didn't feel pressure coming into the Games but I used my aggressive style well to get the win," he added.
"It was hard work but to defend my Paralympic title is a great feeling."
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This is better than an individual gold
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David Roberts on Britain's relay success
There was consolation later on for Roberts, who won his second gold of the Games when he helped the men's 34 point 4x100m freestyle relay team to success.
The team was led off by Matt Walker with Graham Edmunds, Roberts and then 17-year-old Robert Welbourn leading them home in a new world record of 3:59.62.
"This is better than an individual gold," said Roberts.
"We worked hard for each other and this is a great success in our first major final together. It's the best feeling in the world.
"But we couldn't have done it without Marc Woods, who swam in the heats this morning and helped get us to the final and he deserves a lot of credit as well."
Dervis Konuralp finished down in seventh place in the men's S13 100m freestyle.