Sedlacek continued his ground breaking run with victory over Darren Webster.
He hit a 96.5 average en route and he will face Hopp in the penultimate Quarter-Final after winning 6-5 against the Demolition Man.
As usual in Germany, Hopp has the crowd on his side and he saw off Kim Huybrechts in a 6-3 win.
He hit five 180’s and a 96 average en route as he looks to claim another European Tour title this weekend.
Click here for more information about the PDC European Tour, including the format, calendar and the prize fund breakdown.
Afternoon session schedule German Darts Grand Prix:
Michael van Gerwen (106.13) 6-1 (88.76) Stephen Bunting
Ricky Evans (99.44) 4-6 (95.83) Ted Evetts
Rob Cross (110.98) 6-5 (101.91) Daryl Gurney
Mensur Suljovic (94.29) 6-5 (100.14) Dave Chisnall
Karel Sedlacek (96.55) 6-5 (90.02) Darren Webster
Kim Huybrechts (92.6) 3-6 (96.46) Max Hopp
15:00 Ritchie Edhouse v Joe Cullen
15:30 Ross Smith v Simon Whitlock