Complex sentence: During his amateur career, Matthysse fought in the 2003 Pan American Games at Santo Domingo, Dominican Republic, where he went onto stop Colombia's Breidis Prescott in just the first round.
Split into simpler sentences: During his amateur career, Matthysse fought in the 2003 Pan American Games at Santo Domingo, Dominican Republic. Where he went onto stop Colombia's Breidis Prescott in just the first round.