Brown saw off Simon Whitlock in a 6-3 win including two ton plus checkouts en route with the highest being a 147 checkout. The difference came for him on the doubles with 42 per cent hitting 6/14 as he moved through against his former mentor.
Koch on the other hand impressed in a sensational win over Maik Kuivenhoven also by the same scoreline. This was capped off with a roof raising 170 checkout in front of his home crowd in Mannheim.
Robert Thornton also hit the big fish but ended up losing out in a last leg decider 6-5 to Kim Huybrechts.
'The Thorn' should have claimed the victory missing tops for a 134 checkout and Huybrechts sent it all the way and claimed the victory in a frenetic tie which saw the former World Grand Prix champion denied.
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Florian Hempel (77.92) 3-6 (82.22) Simon Stevenson
Jamie Hughes (91.49) 6-5 (90.93) Wesley Plaisier
Keegan Brown (85.46) 6-3 (90.23) Simon Whitlock
Maik Kuivenhoven (89.76) 3-6 (86.64) Karsten Koch
Robert Thornton (92.35) 5-6 (97.35) Kim Huybrechts
Michael Smith v Steve Lennon
Max Hopp v William O'Connor
Jeffrey de Zwaan v Wayne Jones