With victory over Samoa, 2019 tournament hosts Japan have the chance to win the group at a Rugby World Cup for the first time.
Samoa were eliminated from the Rugby World Cup as Japan maintained their 100 per cent record and earned a late bonus point.
Japan will bid to make it three wins from three matches when they tackle Samoa in Toyota City on Saturday, and Michael Leitch is recalled.
Their win over South Africa in 2015 may never be topped, but Japan have once again exceeded expectations with a massive World Cup upset.
Ireland were beaten by Japan without Jack Conan and will now be without the back row for the remainder of the Rugby World Cup.
Japan were knocked out of the 2015 Rugby World Cup having lost to Scotland, and Jamie Joseph fears a repeat despite beating Ireland.
Japan's victory over Ireland at the Rugby World Cup should not be considered a huge upset, according to Rory Best.
Ireland were sensationally upset by hosts Japan at the Rugby World Cup on Saturday, leaving Brian O'Driscoll stunned by their performance.
Ireland's Rugby World Cup hopes took a huge hit as hosts Japan produced another finals shock in Shizuoka.
Japan eased past Russia in their Rugby World Cup opener but will face a far sterner test against Ireland, who will be without Johnny Sexton.