Mr Paytience ($14.20) scored a stylish win in his debut in Sunday's fifth race to give trainer Doug O'Neill a sweep of the 2-year-old California-bred maiden races on the program.
Mr Paytience was always near the front and drew off to win by 7 1-4 lengths over stablemate Nice Haircut in 52.22 seconds.
Mobou, who unseated jockey Gary Stevens in the post parade, closed with interest to finish third after being outrun in the opening quarter-mile. Mobou was the even-money favorite.
Earlier in the day, O'Neill won the third race with Occam's Razor, who was timed in 53.12.
O'Neill has won five races with 2-year-olds at the current spring-summer meeting.