Saruni won the 800m in a national record 1:43.98.
Only Denmark's Kenya-born world record holder Wilson Kipketer has run faster, with times of 1:42.67 and 1:43.96 in 1997.
The 23-year-old Saruni sprinted past American Donavan Brazier in the closing straight to claim victory.
"Oh man, it's crazy," Saruni told NBC television. "I trained hard for this moment. I just had to do it."
Brazier beat Johnny Gray's 1992 U.S. record with a time of 1:44.41, the seventh-fastest ever. Gray had clocked 1:45.00.
Jamaican Kemoy Campbell collapsed while serving as a pacesetter in the men's 3,000m.
Campbell received medical attention on site and was later taken by stretcher for further treatment as the shot put was delayed.
Olympic gold medallist Ryan Crouser won the event with the best throw of 2019, 22.33 metres, as he defeated world champion Joe Kovacs (20.86m).
Germany's Konstanze "KoKo" Klosterhalfen ran away with the women's mile in a national record 4:19.98 and Ajee Wilson clocked the fastest indoor 800m ever by an American, 1:58.60. Both were top performances of 2019.
(Reporting by Gene Cherry in Raleigh, North Carolina, editing by Ed Osmond)
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