Wales triumphed 1-0, a result manager Mark Hughes describes as his best so far thanks to Cardiff striker Robert Earnshaw's strike 12 seconds into the second half.
It completes a notable run of results for a promising Welsh side, who have drawn with Argentina and the Czech Republic in recent months.
While the Germans were without the Bayer Leverkusen contingent, who are preparing for the European Cup final in Glasgow, it was hardly a scratch side. Christian Ziege returned for his first game since suffering a foot injury against West Ham on 13 April.
Wales enjoyed the early chances, but were forced to defend for much of the remainder of the half as Miroslav Klose, Torsten Frings and Ziege all went close.
On the break it was Davies causing the most concern and a minute after the goal he could have doubled the advantage when put in the clear but Oliver Khan produced a world class save to deny him.
Germany pressed in the closing stages, but Wales held firm to record their second ever victory against the Germans.
Wales: Crossley, Delaney, Page, Melville, Speed, Pembridge, Savage, Earnshaw (Coleman 90), Giggs, Davies, Hartson
Germany: Kahn, Heinrich, Linke, Metzelder, Ziege (Bode 63), Hamann (Kehl 73), Jeremies, Deisler (Asamoah 63), Frings, Bierhoff (Jancker 72), Klose.
Simon Davies and Wales put one over on Christian Ziege as Germany were downed in a pre-World Cup friendly in Cardiff.