[2] Moldenhauer won back-to-back German National Championships in 1926 and 1927, and made his third successive final in 1928 where he lost to Daniel Prenn.

In the 1929 French Championships, entering the tournament as the 16th seed, Moldenhauer was the only German to make the fourth round.

He competed in the 1929 Wimbledon Championships and reached the second round, where he lost in five sets to fifth seed Umberto De Morpurgo, an Italian whom he had beaten just weeks earlier in an International Lawn Tennis Challenge rubber.

[4] This put Germany into the 1929 European Zone final against Great Britain, which they won 3-2, with Moldenhauer winning a singles rubber over Bunny Austin.

[4] It was Moldenhauer's final International Lawn Tennis Challenge appearance, meaning he finished with 14 career wins, from 22 matches.