A late Addin Fonua-Blake try gave Tonga a 20-18 win over Samoa before a record 29,411 fans at CommBank Stadium.
Tonga, coached by Dolphins Head Coach Kristian Woolf, secured a semi-final against New Zealand in Newcastle on Friday night.
Samoa also advanced despite the loss, setting up a meeting with Australia. The match will revisit the 2022 Rugby League World Cup final, won 30-10 by Australia in Manchester.
Earlier, England beat Papua New Guinea in Wollongong after building a 22-0 lead, with Dolphins players Herbie Farnworth and Morgan Knowles featuring.
England needed Tonga to defeat Samoa by a significant margin to reach the semi-finals, but the narrow result ended their campaign.
Australia and New Zealand both recorded convincing wins on Saturday. Jack Bostock, a Dolphins outside back representing the Kangaroos, scored a hat-trick as Australia maintained their unbeaten run.
Australia will face Samoa, with Dolphins fullback Hamiso Tabuai-Fidow and forwards Francis Molo and Connelly Lemuelu among those preparing for the match.
Four nations remain, with Dolphins representatives still in contention as the World Cup moves into its semi-final stage.