The Japanese pair pressured the Swedes hard in the third set. But there Källberg and Karlsson showed composure. Four straight points later the match was decided.
The final scores were 11–8, 11–8, 12–10, and the Swedish pair advance to the men's doubles quarterfinals.
A resounding victory: the Swedes are ranked as the world's 185th best doubles pair.
The quarterfinals on Wednesday are expected to be tough - against the fourth-seeded French brothers Alexis and Félix Lebrun.
Karlsson is also still in the singles tournament and will face world No. 8 Lin Yun-ju of Taiwan on Wednesday. Truls Möregårdh is also still in the tournament and will face Denmark's Jonathan Groth.
