Merritt anchored the U.S. team in the 4x400 relay, joining David Verburg, Tony McQuay and Arman Hall for a time of 2 minutes, 58.1 seconds, nearly 2 seconds ahead of silver medalists Jamaica (2:59.88). Russia was third in 2:59.90.
Merritt finished first, with McQuay taking second, in the 400 earlier in the meet.
Friday's win marked the sixth world championship overall for Merritt, who was part of the winning relay teams in 2007, '09 and '11 and also won the 400 in 2009. He was first in both events in the 2008 Olympics.
Farah, running for Great Britain, completed the same double he pulled off last year in the London Olympics, winning the 5,000 Friday in a time of 13 minutes, 26.9 seconds. He earlier won the 10,000.
Ethiopia's Hagos Gebrhiwet was second in 13:27.26 with Kenya's Isiah Kiplangat given the same time but officially in third.
Fraser-Pryce added the 200 to his 100 world championship, again finishing ahead of silver medalist Murielle Ahoure of Ivory Coast. Fraser-Pryce was clocked in 22.17 seconds. Ahoure and Blessing Okagbare, from Nigeria, were both given times of 22.32 but Ahoure was deemed the second-place finisher. Okagbare's bronze medal will go with the silver she won Sunday in the long jump.
Russian Tatyana Lysenko defended her Olympic and world championship titles with a hammer throw of 78.80 meters (258.2 feet). Anita Wlodarczyk, of Poland, was second -- as she was last year at the Olympics -- at 78.46. The bronze medal went the Zhang Wenxiu of China with a throw of 75.58.
German David Storl, who took the gold in the 2011 worlds and was a runner-up in the 2012 Olympics, won the shot put with a heave of 21.73 meters (71.29 feet). Ryan Whiting of the United States was second at 21.57 and Canada's Dylan Armstrong took third at 21.34.
Russia's Aleksandr Menkov had the three best jumps of the day in taking the long jump. His longest was 8.56 meters (28.08 feet), which was the best in the world this year. Ignisious Gaisah, of the Netherlands claimed the silver medal with a jump of 8.29 and Mexican jumper Luis Rivera was measured at 8.27.
The United States continues to lead the medal charts with five gold medals and 16 overall (nine silver and two bronze). The first-place finishes for Lysenko and Menkov gave Russia five gold medals and 11 overall. Kenya, with nine medals -- three of each metal -- is third on the medal chart.
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