Karun Nair (59) and debutant Abhishek Reeddy (54) shepherded Karnataka's innings with a 113-run fifth wicket stand but oce they departed, Karnataka witnessed a batting collapse with the hosts losing their last six batsmen for just 24 runs in the final session of the day. Opener Mayank Agarwal top-scored with a handy 68.
In reply, the Manoj Tiwary-led Rest of India side, who won a good toss on a green Chinnaswamy wicket, were 20 for one at stumps with Jiwanjot Singh (16*) and Paras Dogra (4*) at the crease.
Aaron's lively spell of 6 for 63 gives Rest of India the advantage going into day two but their batsman will have to play out of their skin against a potent Karnataka attack.
With opener KL Rahul ruled out of the game with an injury, Agarwal and the prolific Robin Uthappa opened the innings for Karnataka.
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But Aaron provided Rest of India with a crucial breakthrough early on, dismissing the dangerous Uthappa (10) caught behind in the eighth over.
Nair and Reddy then came to Karnataka's rescue with a solid partnership. A high on confidence Nair after his triple ton in Ranji final looked in good touch and went on to collect 11 boundaries in his 99-ball effort.
But the duo's dismissal off successive balls proved to be the turning point as Aaron and Co ran through the lower-order.
Mumbai pacer Shardul Thakur (1/78) and left-arm spinner Pragyan Ojha (2/62) chipped in at the right time for the visiting outfit.
Brief scores: Karnataka 244 in 77.1 overs (Mayank Agarwal 68, Abhishek Reddy 54, Karun Nair 59; Varun Aaron 6/63). RoI 20/1 in 5 overs.