He was down in 43rd after the ranking round and needed a single arrow shootout to edge his first elimination match with Liu Zhaowu 6-5.
But he turned on his best form when he faced Chen Yu-cheng in the next stage, shooting five inner golds from nine arrows for a dominant 6-0 victory.
'I just want to keep going and try and get as close as I can to what I did before,' said Ruban.
Chen, of Chinese Taipei, had earlier knocked out the final member of Italy's gold-winning team, Mauro Nespoli.
Both Michele Frangilli and Marco Galiazzo had already bowed out following their dramatic win on Saturday and Nespolo lost a decisive fifth set to Chen.
'I do not think the gold had any effect on us,' said Nespoli. 'We worked well and I had two days to get over the gold.
'I thought I could do well and I prepared myself a lot so I am very upset.'
Republic of Korea's Oh Jin-hyek, seeded third after the ranking round, is also through to Friday's knockouts.
He had a simple 6-0 win over Axel Muller first up but was run much closer by Mexico's Luis Alvarez.
Alvarez despatched Yavor Vasilev Hristov in nine arrows before pushing Oh into a fifth-set decider. Oh, who meets Poland's Rafal Dobrowolski next, needed a draw to progress and both men shot 28.
China's Dai Xiaoxiang sent out a warning to the field with two highly-efficient wins.
The seventh seed brushed aside Klemen Strajhar 6-0 and then repeated that scoreline in the last 32 against Luis Eduardo Velez.
Dai missed the gold rings just once in nine arrows against the Mexican, who had come past Iran's Milad Vaziri Teymoorlooei.