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2008 Olympic 400m champion LaShawn Merritt and Grenada's Kirani James comfortably advanced to the 400m semifinals. James, the 2012 Olympic 400m gold medalist, clocked 44.93 seconds, the fastest time in the opening round. Merritt eased to the finish line to win his heat in 45.28 seconds.
Wayde Van Niekerk, who beat Merritt and James at the 2015 World Championships, won his heat in 45.26 seconds.
U.S. sprinter Gil Roberts finished second in his heat to Trinidad and Tobago's Machel Cedenio. The top three in each heat automatically advanced to the semifinals. Fellow American David Verburg was fourth in his heat, but he advanced because he had one of the three fastest times behind the automatic qualifiers.
Refugee Olympian James Nyang Chiengjiek finished his lap in 52.89 seconds, more than seven second behind Lalonde Gordon of Trinidad and Tobago.
The men's 400m semifinals are Saturday at 7:30 p.m. ET, and the 400m final will take place Sunday at 9:00 p.m. ET.