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The problem with India was that once they lost the wicket of Shreyas Iyer, Virat Kohli and KL Rahul became over-defensive and were scoring just 2-3 runs per over. And once Kohli got out, Indian batting lost their balance and were losing wickets quite frequently. And for this match, India didn't had any bowling allrounders. They didn't included Ashwin or Shardul in the XI and as a result the Australians were able to wrap up the Indian innings without much effort.
Here you have the reason why KL Rahul played a really slow innings, many are criticizing the way he played and it is simply because the tail was really weak and India lost wickets and he was not in a position to attack when the pitch was really slow and the ball was not coming into the bat. If the role were reversed and Australia were batting first, they would have struggled the same and batting second would be an ideal situation as it got better in the second half.