Deitermann, 28, scored 32.3 in the dressage, establishing a clear lead of nearly 5 penalties over compatriot Dirk Schrade on the French-bred Anglo-Arab Gadget de la Cerre, who later disappeared from the reckoning after incurring 20pen on the Cross-Country.
German whitewash: Simone Deitermann is flanked by Julia Mestern and Michael Jung on the podium.
Michael Jung and La Biosthetique-Sam FBW, the combination that finished 4th at last year's HSBC FEI World Cup Eventing Final in Deauville, France, were third ahead of Tim Lips (NED), who is causing such a sensation in Dutch Eventing, on Van Schijndel's Owaela, 4th.
German riders were prominent in Deauville, and Kai Ruder and Leprince des Bois, by the Olympic stallion Summersong, 6th there, were 5th in Marbach, while Frank Ostholt (GER) and his 4* horse Air Jordan, 3rd in Deauville, were 7th.
The only other non-German rider in the top 10 was Japan's Yoshiaki Oiwa, 10th on Georgeous George. Oiwa fared better than his trainer, Andrew Hoy (AUS), who incurred 20 cross-country penalties on Grove Joca. Former dual FEI World Cup Eventing finalist Linda Algotsson (SWE) produced one of only four clear Jumping rounds, to finish 11th on the 19-year-old Stand By Me.
Deitermann, who was also ninth on Free Easy NRW, has a long-established partnership with the 16-year-old Flambeau, who was her Young Rider horse as far back as 2002. Recently, they were runners-up in the CIC*** at Fontainebleau (FRA), and last year they were 4th at Boekelo CCI*** (NED), 7th at Luhmuhlen CCI**** (GER) and 3rd in the FEI World Cup Eventing qualifier at Schenefeld (GER).