There is more than one scenario in which Mayank Agarwal might not even have played this Test. Had both KL Rahul and Rohit Sharma been available for selection, they would have opened the innings after having done extremely well in testing conditions in England. They will still likely open in India's next Test.
Even with both of the first-choice openers missing, one of the options to accommodate Virat Kohli was to leave Agarwal because he was not going to be in the first XI in South Africa anyway. It is not known how seriously this option was considered but it never came to pass because Ajinkya Rahane didn't recover from his hamstring strain.
It is tougher to get into the India Test batting line-up than out of it. To start off, they consistently play five bowlers, leaving only five slots for specialist batters. Post 2018, the team management has not fiddled with the three middle-order batters either. So a whole group of talented batters has been competing for just the two slots in an era where opening outside Asia has arguably been the toughest it has been.
It was outside Asia that Agarwal lost his spot at the top after averaging 17 in just four Tests across two series either side of the pandemic-enforced break. It was a ruthless selection call, perhaps unfair on Agarwal. Just the kind of ruthless call newcomers to a successful side have to live with.
Before jumping on Rahane, do remember that as he spent more than 13 consecutive Tests on the bench leading up to his debut, he saw Suresh Raina and Yuvraj Singh come back ahead of him and Ravindra Jadeja get a debut at No. 6 before him. And this was not a winning team. Sachin Tendulkar's retirement eventually opened up a slot for Rahane, and on his last day, at the Wankhede, Tendulkar "told him he might feel hard done by what had happened in his career so far but he should continue to be the way he is, for I was sure [he] would get another chance".
Whether Rahane has reached such a stage in his career is for the team management to decide even if his injury has saved them from confronting it just yet. Given so much talent is vying for just five spots, it is a tough job for the captain and the coach to keep the players from feeling insecure.
"When I was picked here, Rahul bhai came and spoke to me," Agarwal said. "He told me, 'Listen just control what is in your hands. You have this opportunity, go out there, give your best, and that's all we ask of you. And when you get set, make it big.' I am happy. I am happy that when I got set, I could capitalise. But yeah that was very clear from Rahul bhai."
The way Agarwal batted on a difficult pitch and in a difficult situation has shown why it would not have been wise to drop this free-scoring dominating batter against spin. As it stands at the end of the first day of this Test, Agarwal averages 116.4 against spin and scores those runs at 4.04 an over. In spin-friendly conditions, so far he has faced South Africa, Bangladesh and now New Zealand.
This was perhaps the toughest pitch Agarwal has encountered, with the ball turning and bouncing from the middle on day one.
There were also some question marks against him, mainly with his being so late on the ball against the quicks that his toe is still in the motion of coming down when he plays on the front foot. He was nicked off twice, even in Kanpur.
"Yes that is something that I have thought of," Agarwal said of the Kanpur dismissals, "But this innings was more about grit and determination, sticking to a plan, to have the mental discipline to be at that plan, and just be at it. I know there were times when I didn't look good, but it didn't make much of a difference as long as the job was getting done.
"I didn't think of that [his front foot fault]. Mid-series you don't want to be thinking about technique. That's something that even Rahul bhai spoke to me about. He said don't worry about your technique. Just rely on your game plans. That's something I did. This innings was all about grit and determination, and nothing related to technique."
The 120 in Mumbai was a little more than just grit and determination, though. It was about hitting the threatening Ajaz Patel off his lengths because there was a period - especially when he sent back three batters with the score stuck on 80 - when India looked in deep trouble. Ajaz's figures then read 12-7-14-3, having got Cheteshwar Pujara and Kohli for ducks.
Agarwal then took it upon himself to not let Ajaz keep pitching the ball wherever he wanted to. In the left-arm spinner's next over, Agarwal jumped out of the crease and hit his second six. Then he sat back, waiting for the flatter delivery, and pulled Ajaz for four. In an 80-run partnership for the fourth wicket, Shreyas Iyer scored just 18.
Jaffer: 'Fighter' Agarwal 'made the most of a very vital innings'
"Yes it was a conscious decision [to attack Ajaz]," Agarwal said. "It was a plan because I thought he bowled exceedingly well today. He kept bowling in a cluster and he kept putting pressure. Anything that was in our half, the plan was to be a little attacking. Anything that came little towards us in length, I was definitely looking to go. He is somebody who bowled really well, really consistent. He had that phase when he really tied us down, so if we had let him bowl the way he did he would have probably ended with more wickets."
This is the dynamic of Test batting. Outside Asia, the middle order owes a lot to the openers for seeing off the toughest conditions. In Asia, it is on the openers, who start their innings in easier conditions to play the big innings because it is tough to start against the turning ball.
In that regard, Agarwal is proving to be just like Rohit, who also dominates and demoralises opposition spinners. Agarwal has already hit 27 sixes in Test cricket. At home he has gone past the rope 20 times in just nine innings. Rohit has done so 38 times in 27.
What will happen in South Africa is not for Agarwal to control, but it will be difficult to look past Agarwal when Sri Lanka play in his home town, Bangalore. Just as with bowlers, time might be ripe for India to think of horses for courses in batting too.