South African star Petersen won the PDC Africa Qualifier to ensure his spot in the sport’s biggest event, which begins at Alexandra Palace on December 13.
The Mitchell’s Plain thrower overcame Nolan Arendse – the 2015 World Championship qualifier from South Africa – 7-2 in the final.
Petersen also defeated Francois Vertue, Les Gouvela, Rajan Odayar and David Nyemba in the latter stages during a dominant day.
Petersen’s 2018 World Cup of Darts team-mate Liam O’Brien was defeated by 6-5 in the last 16 by Jacques Coetzee.
Arendse overcame Coetzee 6-4 in the semi-finals, after enjoying a win over another former World Cup ace, Shawn Hogan.
Marijanovic won the 2018 German Superleague title with a 10-6 defeat of Dragutin Horvat in Sunday’s finals day at the Maritim Hotel in Dusseldorf.
Marijanovic, who previously competed in the 2013 and 2015 events, will make his third Alexandra Palace appearance next month following the success.
A PDC Tour Card Holder and former World Cup representative for Croatia, Marijanovic overcame Rene Berndt and Stefan Stoyke in the latter stages in Dusseldorf before proving too strong for Horvat.
Meanwhile, New Zealand’s Tahuna Irwin has withdrawn from the World Championship and been replaced by Craig Ross.
Irwin encountered immigration issues ahead of the recent PDC Unicorn World Youth Championship and has now withdrawn from the World Championship.
Ross, the 48-year-old from Ashburton, has replaced Irwin to make his televised debut at the World Championship, having been the runner-up in the DPNZ Qualifier in Invercargill.
Ross has a decade of experience on the circuit in Australia and New Zealand, including his qualification for the 2017 DPA Oceanic Masters.
Following the events in South Africa and Germany, the international qualifying events have now concluded ahead of next month’s World Championship.
The UK & Ireland Women’s Qualifier will be held in Milton Keynes on Sunday, November 25, with the PDC Tour Card Holders’ Qualifier taking place on Monday, November 26 to determine the final places in the field.
2018/2019 William Hill World Darts Championship
PDC Africa Qualifier
Nolan Arendse 6-2 Shawn Hogan
Jacques Coetzee 6-2 Jason Gouvela
Devon Petersen 6-1 Rajan Odayar
David Nyemba 6-5 Angel Morgan
Nolan Arendse 6-4 Jacques Coetzee
Devon Petersen 6-2 David Nyemba
Devon Petersen 7-2 Nolan Arendse
German Superleague Finals
Nico Blum 8-5 Maik Langendorf
Dragutin Horvat 8-4 Manfred Bilderl
Robert Marijanovic 8-4 Rene Berndt
Stefan Stoyke 8-6 Nico Kurz
Dragutin Horvat 9-6 Nico Blum
Robert Marijanovic 9-2 Stefan Stoyke
Robert Marijanovic 10-6 Dragutin Horvat
William Hill World Darts Championship Qualifiers
Top 32 from PDC Order of Merit (at November 26)
Top 32 from ProTour Order of Merit (at November 26)
Plus 32 International Qualifiers:
Two PDPA Qualifiers – November 26
2018 PDC Asian Tour Top Four – Lourence Ilagan, Royden Lam, Noel Malicdem, Paul Lim
2018 PDC Unicorn World Youth Champion – November 25
2018 PDC Unicorn Development Tour Order of Merit top two non-qualified players – Ted Evetts, Geert Nentjes
2018 PDC Unicorn Challenge Tour Order of Merit top non-qualified player – Cody Harris
PDC Nordic & Baltic Top Two – Darius Labanauskas, Daniel Larsson
EADC Champion – Boris Koltsov
Oceanic Masters Champion – James Bailey
DPA Order of Merit Winner – Raymond Smith
DPNZ Qualifier – Craig Ross
German Superleague Champion – Robert Marijanovic
South-West Europe Qualifier – Jose De Sousa
South-East Europe Qualifier – Rowby-John Rodriguez
West Europe Qualifier – Yordi Meeuwisse
East Europe Qualifier – Karel Sedlacek
PDC China Qualifier – Yuanjun Liu
Tom Kirby Memorial Irish Matchplay Champion – Kevin Burness
North American Championship Winner – Jeff Smith
CDC Top Ranked American Player – Chuck Puleo
CDC Top Ranked Canadian Player – Jim Long
PDJ Japanese Qualifier – Seigo Asada
African Qualifier – Devon Petersen
South American Qualifier – Diogo Portela
UK Ladies Qualifier – November 25
Rest of the World Ladies Qualifier – Anastasia Dobromyslova
Indian Qualifier – Nitin Kumar