Shreyas Iyer went to bed at around 11pm on Thursday hoping for and expecting a good night's sleep. He had batted the best part of two sessions in less-then-ideal air so it wasn't really an unrealistic expectation. However, he was awake at 5am, and struggled to catch any more sleep. All the while he kept obsessing about how he was going to bat and how he was going to get to a debut century.

This feeling of sleeping on a score and having the butterflies next morning has become alien to Iyer, who last played a multi-day match nearly three years ago. His ascent to the India limited-overs sides, and the Covid-19 pandemic has made his first-class record almost an afterthought, but as has been repeated in the last few days, it is an impressive record. Ever since ESPNcricinfo has kept strike-rate numbers, no batter other than Iyer has scored 4000 runs at an average of over 50 and a strike-rate of over 80.

Much of that skill, at least against spin and in Indian conditions, was on display during Iyer's debut century. "When I came to Kanpur, I didn't know I was going to play," Iyer said. "Rahul sir [Dravid, the coach] and skipper [Ajinkya Rahane] came to me and said I was going to play [after KL Rahul was ruled out]. Suddenly I had to get into the mindset of red-ball cricket.

"The last match I played was almost three years back, which was Irani Trophy. I took this as an opportunity and a challenge as well. Once you play white-ball cricket for so long, getting back to red-ball cricket is a different ball game. The mindset and routine has to be on point. That's what I focused on rather than thinking about how I am going to play and thinking about who I am going to face on the ground.

"All these thoughts I completely negated. I focused more on my processes. I knew I had the skill. Rahul sir and Ajinkya motivated me a lot. They told me you don't have to change anything because you have played this game before. You have played Ranji Trophy so well, scored so many runs with a really good average. That was my mindset coming to the ground."

This Test debut comes at an interesting time for Iyer. He was a lock for India's T20 World Cup side in 2020 when the pandemic delayed the event. Then he got injured and couldn't play the IPL, which put paid to his chances of going to the World Cup this year. He also lost his IPL captaincy in the process. When least expected came this Test debut, but India's middle order is a crowded place, and he might well have to vacate the spot for the returning captain Virat Kohli for the Mumbai Test. There is a chance India might drop someone else to make way for Iyer, but that is none of his concern right now.

"Sunil Gavaskar sir, when he gave me the cap, told me one important point," Iyer said. "'You don't have to think about your past, you don't have to think about your future. All you have got is present, and you have got to focus on the next ball.' That's what I have been doing throughout. So my aim is to think about today, not think about the next game. If I think about that, I wouldn't be able to perform on the given day. Whatever happens happens for the best, and I will take it in my stride and move forward.

"I didn't look at missing out on the World Cup as an opportunity gone. I was in a good frame of mind. To get this opportunity and to score a hundred in debut Test is a different feeling. I can't explain it. So many messages to me saying this is your best achievement in your life. It took me back to my Mumbai cricketing days."

Back in Mumbai, Pravin Amre, Iyer's former Ranji Trophy coach and also his personal coach, will be waiting for a dinner at his place. Amre, who scored a century on debut himself, against Donald, Schultz, Pringle and McMillan in Durban, had practically demanded one from Iyer.

"Pravin sir, whenever I go for training, keeps on saying you have achieved a lot in life, you have been the captain of an IPL team, you have scored so many runs, but that is in white-ball cricket," Iyer said. "Your main achievement will be when you receive the Test cap. I am sure he would have been really happy when I received the cap. He was like I will only come to your place for dinner if you score a century. So today I will message him and invite him for dinner."

Another man who will be proud in Mumbai is Iyer's father, whose display picture on WhatsApp has for years been Iyer holding the Border-Gavaskar Trophy in 2016-17 after he had been drafted into the squad for the last Test to cover for the injured Kohli. "My dad obviously loves Test cricket the most," Iyer said. "To give him this gift of century would be the best achievement for me. It is a great feeling for both of us. My mom and dad have been really supportive throughout my journey, and they have been the pillars of my success so far and will always be. I would like to thank them and my whole family who have been supportive throughout."