Rio de Los Ciervos went from last to first to capture Saturday's Clasico de Mil Guineas (G1) at Hippodrome Chile by a neck, giving Constitution his second Grade 1 winner in less than a month in the southern hemisphere.
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With 25 black-type horses and 11 graded stakes horses, Constitution leads all Third-Crop sires in both categories this year.
Rios de Los Ciervos was last of 13 3-year-olds for the first half of the trip. Going wide while passing horses on the final bend, it wasn't until deep stretch that he took the lead, outrunning El Notable in the final strides to claim victory in the 1,600 meter race.
The winner was bred in Chile by Don Alberto and is out of Gran Pelicula, who is a half-sister to two-time champion Don Gabino.