Mercedes-Benz sales fell 8.2% year on year in September to 202,819 vehicles worldwide. Nine-month volume slipped 0.1% to 1,715,087 units.
Third quarter 2018 volume was also down 8.2% to 526,255 vehicles.
Daimler noted Mercedes-Benz certified its entire fleet for Europe according to the WLTP standard from 1 September with certified vehicles already on their way to retailers.
September sales were also affected by delays in certification in some export markets and by model changes.
It nonetheless claimed premium brand leadership in th UK, Italy, France, Russia, Switzerland, Portugal, Sweden, Turkey, Japan, Australia, the US and Mexico.
Europe sales fell 9.4% to 91,609 vehicles in September and by 4.7% to 688,956 year to date.
German sales fell 16.7% to 22,780 cars last month and 5.6% to 217,943 YTD.
Asia Pacific region sales rose 8.1% to a new record 714,598 units YTD though September volume fell 4.4% to 75,414.
China saw a record September tally of 54,632, up 6.9% with YTD sales up 13.1% to 500,707.
NAFTA region sales fell 9.9% to 31,273 last month while YTD volume was down 6% to 271,944.
US September sales fell 9.8% to 26,169 and 7% to 225,384 YTD.