They join former finalists Adelaide United and Uzbekistan's Bunyodkor after edging out Japan's FC Tokyo 1-0 on Wednesday.
Tournament debutants Guangzhou became the first Chinese side to reach the quarter-finals of the AFC Champions League since 2006 as a first half goal from Brazilian striker Cleo was enough to end Japanese interest in the competition.
Also on Wednesday, Ulsan had earlier recorded a 3-2 win over J.League champions Kashiwa Reysol after Australia's Adelaide had beaten Japan's Nagoya Grampus 1-0, while the same scoreline was enough as Bunyodkor ended the hopes of 2010 winners Seongnam Ilhwa Chunma.
After a goalless first half in the Round of 16 encounter, the Korean side took a deserved lead through a Kim Shin-wook header only for Leandro Domingues to draw the sides level midway through the second half.
Ulsan regained the lead courtesy of an own goal from Naoya Kondo and extended their advantage through Lee Keun-ho before Junya Tanaka pulled back a goal for Kashiwa in stoppage time.
"It was difficult game but we are happy with this win as we are the only survivors among the four K-league teams taking part in this year's competition," said Ulsan coach Kim Ho-gon.
"I have told my players many times that we are not only representing our club but that we are also representing Korea and the players recognise the importance of that."
Adelaide, who lost the 2008 final to Japan's Gamba Osaka, had themselves kept alive Australian interest in the AFC Champions League as Jon McKain's first half strike saw secured a hard-fought 1-0 win over Nagoya on Tuesday.
And with Saudi Arabian trio Al Ittihad, Al Hilal and Al Ahli along with Iran's Sepahan already safely through to the last eight having posted wins in the Round of 16 last week, the draw for September's quarter-finals will take place on June 14.