The top seed Fritz defeated Australian player Aleksandar Vukic 7-5, 6-7(5), 6-4 in the championship match to win the ATP 250 title in his first match on home soil since March.
Zverev, a confident 19-year-old who had defeated top seed Casper Ruud in the quarterfinals, gave Fils little opportunity to catch his breath with a hard-hitting, big-serving performance on the German clay in their first Lexus ATP Head2Head match.
Wawrinka has been impressive in his first appearance in Umag since 2007 and has won all six sets played at the clay-court ATP 250 event. He aims to clinch his first tour-level title since Geneva in 2017.