McMorris, 32, fell in two of three attempts despite qualifying third. He had been cleared to compete last week after suffering a concussion, bone bruising near his pelvis and an abdominal strain in a crash during training.
The 20-year-old Spalding, the 2024-25 World Cup champion, finished two spots behind his countryman. China's Su Yiming won gold on his 22nd birthday, with Japan's Taiga Hasegawa earning silver and American Jake Canter taking bronze.