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Jernigan won the US national singles title three consecutive times in 1983-85. Representing Harvard University, he won the US intercollegiate singles title three times in 1983-84 and 1986. He also helped Harvard win several team titles and was a four-time All-American.
In 1994, Jernigan won the men's doubles title at World Hardball Doubles Championship (partnering Jamie Bentley).
Outside squash, Jernigan has worked as the head of investment banking at Jefferies bank.