Ward and his horse Clinta kept cool under pressure and blistering heat to put the hosts top the podium in front of raucous flag-waving home crowd at the Tryon International Equestrian Center.
Sweden settled for silver while Germany took bronze.
The first jump off to decide a world championship team competition almost needed another round with Sweden having posted three clean rides and one fault while the U.S. had two clean rounds and one fault.
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That left everything riding on McLain, who helped the U.S. to gold at the 2004 and 2008 Olympics and a silver at the Rio Summer Games.
McLain, the last competitor in the ring, needed not only a clean round but a fast time and he stepped on the gas heading into the final barrier to give the U.S. gold by a wafer-thin two seconds.
It was sweet redemption for McLain, who had been the second last rider in the medal round and knocked down a barrier that sent the gold medal to a jump off.
"I knew the situation going in, I knew a clear would win and I couldn't have a time fault," said McLain, who was joined on the podium by two-time Olympian Laura Kraut and newcomers Adrienne Sternlicht and Devin Ryan.
"I was given two chances to win this thing and I am very grateful I have such a great team also delivering great scores.
"I got a second opportunity to help our team win.
"In that moment you have to do your best, it's the only thing that is in front of you."
It marked the first time U.S. had claimed world championship gold since 1986 in Aachen.
Germany's bronze was their sixth medal (three gold, one silver, two bronze) in team show jumping tying France for the most world championship medal in the event.
The top six teams all qualified for berths at the 2020 Tokyo Olympics, the U.S., Sweden and Germany joined by Switzerland, the Netherlands and Australia.
(Editing by Nick Mulvenney)
