India are in a strong position as Sri Lanka were reduced to 86/6 at stumps on Day 1 trailing by 166 runs in the second Test being played at the M Chinnaswamy Stadium in Bengaluru.
Bowlers dominated the day with 16 wickets falling in the entire day.
The visitors made early inroads on a spinner-friendly track with the second Test heavily tilting in favour of the hosts.
The bright afternoon sun in the beginning of the day/night contest did not allow the pink ball to swing enough and trouble the batters but the early and sharp turn on offer made life tough for the Indians, who were tottering at 126 for five at one stage.
Rishabh Pant began the counter-attack with his fiery 36-run knock and Iyer carried forward the recovery work with his scintillating 92-run knock that helped India post a decent 252 in their first innings.
Iyer's entertaining knock, that came off 98-balls and had 10 fours and four sixes, negated all the good work done by the visiting bowlers in the first session when they had taken four wickets, including that of skipper Rohit Sharma (15) and Virat Kohli (23).
Iyer missed out on what would have been a deserving second Test hundred as he was stumped off left-arm spinner Praveen Jayawickrama (3/81) while going for a big shot.
Later, the pink ball was expected to assist the fast bowlers in comparatively cooler floodlit conditions and the lethal India pace duo of Jasprit Bumrah (3/15) and Mohammed Shami (2/18) blew away the top-order with two wickets apiece.
Shami's dismissal of rival captain Dimuth Karunaratne (4) was a treat to watch as the ball came in to shatter the stumps.
Sri Lanka ended the day at 86 for six, trailing by 166 runs, as 16 wickets fell on the opening day with nine of them taken by the spinners.
Old warhorse Angelo Mathews (43 off 85 balls) and Charith Asalanka (5) had a 22-run stand for the fifth wicket but it did not last long with Axar Patel getting rid of the left-hander.
Mathews twice lofted Axar for straight sixes and negotiated the other Indian bowlers with confidence but his colleagues were found wanting due to lack of technique and temperament to counter a world class Indian attack on a tricky surface.
Mathews' combative knock ended when he fished outside off stum and edged one from Bumrah to Rohit in second slip.
Niroshan Dickwella (13) and Lasith Embulkdenya (0) will resume Lankan innings on Sunday.
The sharp turn that Sri Lankan bowlers derived off the pitch coupled with the unpredictable bounce reminded of the Ahmedabad pink-ball game, where Indian spinners ruled the roost to win the game inside two days.
The world cricket is yet to see a pink-ball game, out of 18 played so far, lasting the full distance. The games under flood lights, as of now, are being dominated by the bowlers and they won't complain.
Not even a tinge of green on the track at M Chinnaswamy stadium, India expectedly opted to bat even as Rohit, who looked fluent, and Mayank Agarwal (4) could not utilise the opportunity to score big.
Exploiting the conditions to the maximum, the visiting bowlers, especially left-arm spinner Lasith Embuldeniya (3/94) kept the Indian batters guessing and close to 25,000 fans on tenterhooks.
While Hanuma Vihari applied himself during his knock of 31 (off 81 balls), for Pant (39 of 26 balls) counter-attack was the best strategy. He went about his business in his own style while Iyer, as usual, was impressive with his controlled aggression.
Both Pant and Iyer ensured that Lankans do not run away with the opening day honours, taking the fight to the rival camp with their fearless batting.
However for Kohli, who is chasing an elusive Test hundred for more than two years now, all the hard work of carefully crafted knock was undone by a Dhananjaya de Silva-delivery that kept low and trapped him plumb in front when he tried to play on back-foot.
The former skipper, who was driving and cutting the ball with confidence, stood there in disbelief that the mischief of the pitch dictated his return back to the pavilion.
He trudged back, ruing another opportunity lost. Not that he lacked skill or the bowler produced something extraordinary but for sheer unpredictability of the 22-yard strip at M Chinnaswamy stadium.
Vihari's eventful stay was ended by Praveen Jayawickrama, also a left-arm spinner. He and Kohli (23) confidently played drives and cuts to raise a 47-run stand for the third wicket.
Pacer Lakmal maintained a probing off-stump line but left-arm pacer Vishwa Fernando largely kept it on middle and leg, from where Rohit easily played on-drives. Agarwal, who dispatched one over-pitched from Lakmal to cover region boundary to start off, threw away his wicket when he got himself run out in the second over of the day.
Left-armer Fernando dug one short and the Indian skipper dispatched that with ease into the spectators' stand with his trademark pull shot.
Embuldeniya created a chance in his very first over when he induced an edge from Vihari but it just fell short of first slip.
However, he scalped the Indian captain, getting him caught in the second slip. The ball had turn and bounce as it took the edge and flew towards Dhananjaya de Silva, who completed the catch at gully.
Vihari survived when umpire judged him leg before off Jayawickrama but the DRS review showed that the ball was missing the leg stump. He was 31. However the same bowler had him caught behind soon.
India were struggling but Iyer changed the complexion of the game for the hosts.
