Under Coach DeGara, a 1956 Olympic Gold Medalist for Hungary, the dominant Serra High swimming team would receive a ranking of second in the nation and win the Catholic Athletic League Championship eight times consecutively from 1967-1974.

[3][6] At the Central Coast Section Championships at Foothill College on May 10, 1969, McBreen won the 400 freestyle, a signature event, with a time of 3:42.0 leading Serra High to second place behind the powerful Santa Clara team.

[8] In stiff competition in July, 1970, a month after graduating Serra High, McBreen announced his arrival by finishing ahead of Hall of Fame Olympian Hans Fassnacht and winning the 200 freestyle at the Santa Clara Invitational Meet with a time of 1:56.98, though Mark Spitz had been scratched from the event.

[4] At the late March 1972 NCAA Championship at West Point, McBreen, swimming third leg, helped his relay team set a record of 6:38.635 in the 4x200-meter freestyle with fellow Trojan swimmers Ed McCleskey, Steve Tyrrell, and Jim McConica.

Because American Rick DeMont, who won the gold, became disqualified when it was ruled his asthma medication was unauthorized, McBreen moved up a place and was awarded the bronze medal.

He attended University of Southern California's Medical School, performing his residency at Ventura's County General Hospital and specializing in family medicine.