On paper Sasaki should be the favourite, just from comparing records, however he is 40 years old and has only fought 6 professional rounds in the last 3 years, easily seeing off Tatsuya Miyazaki back in February. The veteran is also the naturally smaller man, as seen by the fact Okazaki towered over him at the weigh in.
Whilst Sasaki is an inactive old man he is a teak tough fighter who gives anyone problems and won't be coming in to the bout intimidated, in fact he seems to be viewing this bout as a potential stepping stone towards a title bout.
Okazaki amazingly began his career as a very tall Featherweight but quickly grew into his body and has fought as high as Welterweight. His crowning achievement so far is beating Daiki Koide and he has also fought for an OPBF title, losing to Keita Obara last year. Aged 29 he's much younger than Sasaki but given his his losses through his career he is limited and hasn't won a bout since November 2014.
(Image courtesy of boxingnews.jp)