Murphy finished in 51.97 seconds, three-hundredths of a second off the record set by Aaron Peirsol in 2009.
Murphy is continuing America's dominance in this event, in which he won the sixth consecutive gold medal for the USA.
And in other drama, America's Lilly King beat Russia's Yulia Efimova to win the gold in the 100-meter breaststroke at the Olympic Aquatics Stadium in one of the most anticipated contests of the Olympic Games.
King finished in 1 minute 4.93 seconds, more than a half-second ahead of Efimova.
"Tonight has been so crazy," King said. "I'm a gold medalist and it's what I've always wanted to be and it's an incredible feeling.
"I'm probably going to start crying. I'm usually not a crier but this is a special moment so we'll see if it gets to me or not."
After the race she said that her win was an affirmation of her "clean" approach to competing.
She told an interviewer that her win was a statement "that we can still compete clean and do well at the Olympic Games and that's how it should be."
Efimova, twice banned for doping, was once again loudly booed before the race. She's become a symbol at the Games of frustration over Russia's state-sponsored doping scandal.
Meanwhile, Sun Yang of China, won the gold in the men's 200-meter freestyle; Sun finished in one minute and 44.65 seconds
Hungary's Katinka Hosszu, took the gold in the women's 100-meter backstroke. Nicknamed the "Iron Lady," Hosszu had considered quitting after a disappointing London 2012, admitting to suffering depression.
Japan's gymnastic triumph
Japan's Kohei Uchimura -- "Superman" to his fans -- is widely considered the world's greatest gymnast. The reigning Olympic individual champion also has 10 world championship gold medals in his collection.
An don Monday he led the Japanese men -- alongside Ryohei Kato; Yusuke Tanaka; Koji Yamamuro; Kenzo Shirai -- to gold.
He told CNN before last year's world championship: "I want to create beauty that nobody else can express. I want people who do gymnastics -- and those who don't -- to watch and notice there is something different about my performance."
There was other drama too that had little to do with athletic prowess.
Olympics officials had to apologize after they raised incorrect Chinese national flags during medal ceremonies.
The Chinese flag is red and features a large yellow star flanked by four smaller stars. But the smaller stars on the flag used in the Games were aligned incorrectly -- parallel to each other, like the stars on the American flag.
On the correct Chinese flag the four smaller stars should be rotated so that they point toward the center of the larger star.
"We do understand that there is a problem with the flag," said Mario Andrada, Rio 2016 Olympic Games executive communications director, on Monday. "It's very small. You have to be very familiar with the Chinese flag to understand that. However, we need to correct it."
Viewers in China spotted the mistake and took to Sina Weibo -- a Chinese social media site -- to complain, according to China News Service (CNS), the state-run news agency.
At least Rio officials aren't alone in their China flag flub. On Saturday, Australia's Channel 7 network displayed the Chilean national flag on air -- instead of the Chinese flag.
Outside the stadium, Brazilian police have been working to dismantle an international gang of ticket scalpers.
On Monday, they arrested two people in relation to scalping Olympic tickets and selling fake ones. In a statement, Brazilian Civil Police says it arrested British citizen Kevin James Mallon and Barbara Carnieri.
Mallon is one of the directors for THG, a British ticket reseller. In 2014, THG, CEO James Sinton was arrested by police in relation to a scalping ring for FIFA World Cup tickets.
Carnieri, arrested along with Mallon, is also an employee of THG. She had been hired by the British company to act as an interpreter during the games. Police say she is being charged with marketing by ambush.
It is illegal in Brazil to resell tickets for anything higher than face value.
• Rugby Sevens (Women) Gold -- Australia 24, New Zealand 17.
• Weightlifting (women 58 kg) Gold -- Sukanya Srisurat, Thailand
• Weightlifting (Men's 62 kg) Gold - Oscar Albeiro Figueroa Mosquera, Colombia
• Shooting (Men's 10 m air rifle) Gold--Niccolo Campriani, Italy, 206.1
• Shooting (Men's trap final) Gold--Josip Glasnovic, Croatia.
• Judo (Men's 73 kg) Gold -- Shohei Ono, Japan, defeating Rustam Orujov, Azerbaijan.
• Judo (Women's 57 kg) Gold -- Rafaela Silva, Brazil, defeating Sumiya Dorjsuren, Mongolia.
• Fencing (Women's individual saber) Gold -- Yana Egorian, Russia, defeating Sofya Velikaya, Russia, 15-14.
• Diving (Men's synchronized 10 m platform) Gold -- China (Lin Yue; Chen Aisen)