The 29-year-old old Merritt was the fastest man over lap race clocking season's best time of 44.36 seconds for the win and beating Grenada's Bralon Taplin who posted 45.28. Aldrich Bailey of the United States concluded the podium with 45.38 seconds.
Women's 400m race took Sanya Richards-Ross with a blistering time of 50.47 seconds ahead of compatriot Jessica Beard 51.03.
American hurdler Tiffany Williams posted a very fast time of 54.33 winning the 400m hurdles.
Jamaican Simone Facey clocked 22.55 seconds edging USA's Shalonda Solomon 22.56 for the win, while world championships medalist Wallace Spearmon of the United States clinched victory in the men's 200m in 20.12.
World record holder and Olympic champion in decathlon Ashton Eaton beat the field in 110m hurdles 13.38 seconds.
Maggie Vessey was the winner in the women's 800m race with a time of 2:00.16.
01 December 2022 22:30 (GMT)
04 December 2022 08:00 (GMT)
04 December 2022 15:00 (GMT)