Gautam Gambhir, a former India opener and 2011 Men’s ODI World Cup-winning team member, believes the opening match against Australia will be crucial for Rohit Sharma’s team to win the trophy. India, the champions of 1983 and 2011, will begin their quest in the 13th edition of the Men’s ODI World Cup on October 8 at the MA Chidambaram Stadium in Chennai.