After trailing 1-0 from the first round, Keita - who has struggled with a knee injury since reaching the quarter-finals of the Beijing 2008 Olympics - hit back to lead 4-1 and then landed head kicks in the third to complete a 13-4 win over the seventh seed, who had won silver at last year's World Championships.
Keita, though, faces a stern test in the last eight against Canada's number two seed Francois Coulombe-Fortier.
'I feel well, but that was just the first fight and the first match of the morning is always difficult. Now I know what to do from the next rounds on and hopefully I'll get through to the end of the tournament,' he said.
'I got injured in my knee and I'm trying to get back to the top level.'
Defending Olympic champion Cha Dongmin of Republic of Korea also moved into the quarter-finals with a 9-4 win over Ivan Trajkovic of Slovenia and will face eight-seeded Turk Bahri Tanrikulu in the afternoon session.
He said: 'I trained a lot for these Olympic Games, but at the beginning of the match my body was not relaxed, I was a bit tense.'
World champion Anne-Caroline Graffe, the top seed from France, booked her quarter-final place in the women's +67kg with a 17-9 win over Uzbek fighter Natalya Mamatova after a strong final round.
'I don't fight thinking that I'm the world champion, because it would be too much pressure on me,' she said.
'The Olympic Games are way too important, so if I think about them, it's not good.'
Beijing 2008 Olympic champion Maria del Rosario Espinoza edged past Cambodian Davin Sorn 3-2 with a late body punch in the third round.
Fourth seed Wiam Dislam of Morocco is out, though, after she was beaten by Cuban Glenhis Hernandez on sudden-death point.