The pair of 25-year-olds have squared off since their teenage years. The Americans faced each other for the first time -- when Fritz was 13 and Paul was 14 -- at the 2011 USTA Boys' 14s National Championships in San Antonio.
On Friday, Paul need nearly three-and-a-half hours to beat the third-seeded Fritz in the semifinal round and became the third American to reach the final in Acapulco. Fritz accomplished the feat in 2020, and Sam Querrey won the tournament in 2017.
Paul, who reached the semifinals in the Australian Open in January, is trying to capture his second career title after Stockholm in 2021.
The eighth-seeded De Minaur is 3-0 against Paul and will play in his first final since Atlanta in 2022, when he won his sixth career title.