Australian Open doubles champion Thanasi Kokkinakis won a decisive singles rubber to power 28-time winners Australia through to the next stage of the Davis Cup on Saturday. South Korea toppled Austria to also make the grade. Lleyton Hewitt’s Australians went into day two tied 1-1 with Hungary and were fighting an uphill battle after Fabian Marozsan and Mate Valkusz upset John Peers and Luke Saville to clinch the doubles 6-4, 6-4. That left world number 30 Alex de Minaur needing to win against 35th-ranked Marton Fucsovics to keep the clash alive and backed by a rowdy crowd at Sydney’s Ken Rosew…