Indian bowlers received an absolute beating from the Australian batters on Tuesday evening in Mohali which led to the visitors chasing down a big target of 208 runs with 4 wickets and 4 balls to spare, and take a 1-0 series lead.
Opening for the first time in international cricket, Cameron Green clattered 61 runs off 30 balls, supported by Finch (22 off 13) and Smith (35 off 24). All the Indian bowlers, barring Axar Patel (3/17) went for 11 or more runs per over, continuing their dismal defensive show from the Asia Cup.
Here are the 3 big mistakes that cost India the Mohali T20I vs Australia:

Bhuvneshwar Kumar’s expensive death overs again: It’s a bit difficult to accept and would be really challenging for the management as well – but Rohit Sharma will have to realize that Bhuvneshwar shouldn’t bowl the 19th over anymore while defending.
This is three games now where Bhuvneshwar’s poor 19th over has left too little to defend in the last over: 19 runs vs Pakistan, 14 runs vs Sri Lanka, and today, vs Australia, he conceded 16 runs in the 19th over and 15 runs in the 17th over.

Bhuvneshwar is still India’s best new ball bowler, but Rohit should complete his 4 overs by the 16th over.
3 dropped catches: ‘Catches win matches’ – yes. But dropped catches could cost you matches – yes. India dropped 3 catches today – 2 which should have been taken, and one was a tough return catch to Harshal, the bowler.
Axar Patel dropped Cameron Green in the 8th over when Green was on 42. In the next over, KL Rahul dropped Steve Smith, who was on 19 at the time. We know what these two did: make significant contributions after being given a reprieve.

Then, in the 18th over, Harshal Patel was offered with a difficult return chance by Matthew Wade, but Harshal dropped it. Wade was batting on 23 (14) when he gave that opportunity; he smashed 22 off the next 7 deliveries.
Missed taking review of Cameron Green: this one would also hurt India. On the third ball of the 5th over, bowled by Chahal, Green, batting on 17 runs, moved inside the line and misses the sweep, and was struck on the pad. Chahal and keeper Dinesh Karthik barley appealed, which was turned down as it seemed to slide down leg.
However, the replays showed that the ball was crashing into the leg-stump. India missed a big opportunity to dismiss Green early on, and the result could have been different had they taken the review.