Steve Smith struck a resolute unbeaten 117 while Glenn Maxwell hit a career-best 82 on his Test comeback as they ended day one at a solid 299 for four after winning the toss.
"I think tomorrow first session is going to be one of the most crucial in this match. If we can win that session then we go a long way in winning the Test match," Renshaw said.
The southpaw praised his skipper for making his bat talk after the DRS controversy in the Bengaluru Test.
Twenty20 specialist Maxwell who replaced the injured Mitchell Marsh at number six grabbed the opportunity with both hands with unbeaten half-century. Boasting a T20I strike rate of 167.41, Maxwell stood out with his controlled shot-selection.
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Renshaw said batting is tough when the bowler gets reverse swing.
"I think when the ball is reversing it just has to do a little bit to show how hard it is out there. But they bowled quite attacking, in terms of stump-to-stump with the reverse balls. I think they bowled well with the reverse ball and got a few wickets with it."
Asked whether India dropped intensity after the injury scare to skipper Virat Kohli, he said: "I wouldn't say intensity. They still came out pretty hard. But I think there probably wasn't as many words out there today. They still played pretty hard cricket and made it tough for us."