Complex sentence: The Monarchs' only loss was to Long Beach Poly; in the CIF Southern California Division I regional final, Mater Dei defeated Long Beach Poly when Jason Quin sank a buzzer beating three pointer at the Los Angeles Sports Arena.
Split into simpler sentences: The Monarchs' only loss was to Long Beach Poly. This loss was later avenged in the CIF Southern California Division I regional final, when Jason Quin sank a buzzer beating three pointer to defeat Long Beach Poly at the Los Angeles Sports Arena.