Yamaguchi akakwikwidza semunhu ane makore gumi nemasere uye nhengo yechikwata cheJapan mumitambo miviri ye freestyle relay pa2008 Summer Olympics muBeijing. Pasinei nokurasikirwa nenzvimbo yega yega mumamita mazana maviri akasununguka, akakwanisa kutora nzvimbo yechina mumitambo yeOlympic muTokyo (2: 01.64) kuti awane sarudzo yakananga pachikwata chevarwi. Kushanda pamwe chete naHaruka Ueda, Maki Mita, naEmi Takanabe mu 4 × 200 m freestyle relay
Pakupedzisira, Yamaguchi akahwina muchikamu chechipiri nokuparadzaniswa kwe1:58.51, asi chikwata cheJapan chaifanira kugutsikana nenzvimbo yechinomwe muna 7:57.56. Yamaguchi akapindawo mumakwikwi e4 × 100 m freestyle relay, pamwe chete naUeda, Mita, naAsami Kitagawa, asi akatadza kupinda mumakwikwi e8 epamusoro ne0.08 yechipiri munguva yekutanga ye3:39.25.