Both teams now sit on four points in Group H but still have work to do if they wish to secure a spot in the knockout stages of the competition.
Senegal began the match on the front foot with Mane failing to provide a clinical touch by the penalty spot as early as the second minute, but it did not take long for the Liverpool attacker to open the scoring.
A cross from the right was only half-cleared into the path of Youssouf Sabaly and after the full-back's shot was parried by Eiji Kawashima, the ball rebounded off Mane - who was no more than four yards out - and into the bottom corner.
Japan were struggling to cope with Senegal's superior strength, but the African side were also impressing in the final third and Alfred N'Diaye could have done better with a volley after meeting Wague's cross.
As the game went through the half-hour mark, Japan had offered little in the final third but an equaliser was found 11 minutes before the break as Inui benefitted from smart build-up play from Yuto Nagatomo before curling the ball into the far corner from 16 yards.
Japan started to play with confidence but Senegal should have regained their advantage just before the break after M'Baye Niang was played through on goal. However, rather than lob Kawashima - who was out of his goal - the Torino striker tried to volley to his right and the goalkeeper made the save.
After the restart, both teams wasted little time in going on the offensive with Yuya Osako sending a header too close to N'Diaye from around eight yards before Niang volleyed over from distance at the other end.
On the hour mark, Japan should have taken the lead when the ball was delivered into the six-yard box where Osako was waiting, but the FC Koln striker missed his kick at the near post.
Soon afterwards, a neat move led to Japan striking the woodwork through Inui, who curled the ball onto the top of the crossbar from just inside of the area, but just as Japan were setting the pace, Senegal went back in front.
Sabaly's low cross from the left was flicked on by Niang and Wague was waiting at the back post to lash the ball into the roof of the net for his first international goal.
Japan opted to introduce Honda and shortly after his introduction, the national team legend scored his 37th goal for his country - and became the first Japanese player to net at three World Cups - when he was perfectly placed to tap home Inui's cutback after Senegal had made a mess of a cross delivered from the right.
Both teams continued to look for a fifth goal of an entertaining contest - one which could have potentially secured qualification for the last 16 by the end of the night - but Akira Nishino and Aliou Cisse had to be content with their sides retaining their respective unbeaten records.
JAPAN (4-5-1): Kawashima; H Sakai, Yoshida, Shoji, Nagatomo; Shibasaki, Hasebe, Haraguchi (Okazaki 75'), Kagawa (Honda 72'), Inui (Usami 87'); Osako
SENEGAL (4-3-3) K N'Diaye; Sabaly, Sane, Koulibaly, Wague; Gueye, A N'Diaye (Kouyate 65'), B Ndiaye (Ndoye 81'); Sarr, Mane, Niang (Diouf 86')