Lauding India's 31-run victory over Australia in the first Test in Adelaide, former captain Sourav Ganguly on Monday predicted the series will be a hard-fought one and all four rubbers will yield results."It's an excellent win. Really credible," Ganguly told reporters at the Cricket Association of Bengal (CAB) premises.Chasing 323 for victory, Australia's lower middle order gave a tough fight in their second innings against an inspired Indian bowling attack before being eventually bowled out for 291 just before tea on the fifth and final day.This is India's sixth Test win on Australian soil and is the first time they have won a series opener in Australia.India had posted 250 in the first innings riding Cheteshwar Pujara's 123 with Australia managing 235 in reply as Ravichandran Ashwin and Jasprit Bumrah grabbed three wickets apiece.In the second innings, Pujara (71) starred with the bat once again as India made 307, setting the hosts a daunting target, to which they fell short. For the Aussies, off-spinner Nathan Lyon grabbed six wickets while India's Bumrah, Ashwin and Mohammed Shami bagged three wickets.India have never won a Test series in Australia with their best result being a 1-1 draw in the 2003-04 series under Ganguly.There are three more Test matches to go and Ganguly predicted every match will have a winner."It will be a competitive series. There will be a result in every match."India will next play in Perth from Friday.