Leon Goretzka started the game in Belfast, lasting 66 minutes in what was his eleventh international appearance.
Sebastian Rudy, Sandro Wagner and Joshua Kimmich scored the goals for the reigning holders, who qualify for their 19th consecutive World Cup. Josh Magennis scored the consolation goal for the hosts three minutes before the end.
Goretzka and Co. face Azerbaijan in the final group match on Sunday, 8th October (20:45 CEST) in Kaiserslautern. A win would see Germany complete the perfect qualifying campaign with 30 points. The groups will be drawn on 1st December during a ceremony in the concert hall of the Kremlin Palace in Moscow.