The victory gave Mayer his second career title after Bucharest in 2011. The 32-year-old German missed nearly a year-and-a-half with an adductor tear and had dropped outside the top 200. He even considered retiring.
Zverev is considered to be one of the brightest prospects on the tour. The 19-year-old German is the highest-ranked teenager on the tour at No. 38. He was seeking his first title. Zverev had beaten top-seeded and eight-time defending champion Roger Federer in the semifinals.
Zverev saved two match points to force a third set, but Mayer broke serve again for 4-2 and his steadier game brought him the title on his fifth match point.
Teenager Alexander Zverev caused a major shock as he beat eight-time winner and top seed Roger Federer in the Halle grasscourt semi-finals on Saturday.
Error-strewn Federer’s vulnerability on his favourite surface could perhaps be explained by a back injury that made the 34-year-old miss last month’s French Open, but this was not the build-up to Wimbledon that the Swiss ace wanted.
The 19-year-old Zverev triumphed 7-6 (7/4) 5-7 6-3 to reach only his second ATP Tour final after being beaten by Dominic Thiem on clay in Nice last month.
The veteran Federer, a 17-time Grand Slam winner, won the last three Halle Open tournaments but he met his match in the spirited world number 38.
Just over a week before the start of Wimbledon, it was the second semi-final defeat in a row on grass for the world number three after Thiem beat him in Stuttgart last week.
Federer hasn’t won a Grand Slam since Wimbledon in 2012 and given the form of world number one Novak Djokovic, Federer’s current level would unlikely see that run come to an end.
Zverev is already guaranteed to improve his career-high ranking in Monday’s new list to inside the top 30.
He took the first set on a tie-break having lost just four points on serve and firing 14 winners.
It was Federer’s first defeat to a teenager in almost 10 years.