"I made him promise me before he left. I made him promise me that he will finish the World Cup with the most runs. If he gets it, I told him I'll gift him a car."

That's Jwala Singh, Yashasvi Jaiswal's coach, talking to ESPNcricinfo inside Chalet 26 of Potchefstroom's JB Marks Oval, watching his protege take a big step in fulfilling that promise, with a century against Pakistan in the semi-final on Tuesday.

Jaiswal, however, has no idea Singh is in South Africa. Jaiswal had categorically told Singh not to come for the tournament. But Singh couldn't resist, so he flew to Johannesburg and then drove to Potchefstroom as soon as India's semi-final spot was confirmed. He stays hidden all day, away from Jaiswal's line of vision, just in case his student gets distracted seeing his coach.

But Singh is more than Jaiswal's coach. Since Yashasvi's father handed over his son's responsibility to Singh in 2013, Yashasvi has lived with his coach in Mumbai. Effectively, Singh is the father figure in Jaiswal's life. The love is on display as Singh gets up from his deck chair to clap as soon as Jaiswal scores the run that takes him past Sri Lanka's Ravindu Rasantha as the tournament's highest run-scorer.

The Jaiswal at the Under-19 World Cup, though, is very different from the Jaiswal in domestic cricket. Back in India, the left-hand batsman has built a reputation of being an attacking batsman. He has already struck double-hundreds twice in one-day cricket, once for Mumbai Under-19 and another for the senior Mumbai team. But at the World Cup, he has been restrained. Against Sri Lanka, his 59 came at a strike rate of 79.72. Against New Zealand, his 57 was scored at a strike rate of 74.02. Against Australia in the quarter-final, his strike rate was 75.60 while scoring 62.

"In Mumbai, he has senior cricketers around him, so he has the freedom to play his natural game. But here, he knows he's probably the most crucial part of the team's batting," Singh explains. "That's what makes Jaiswal special - his adaptability."

Fifteen minutes later, Jaiswal guides a short ball down to the fine-leg boundary to inch closer to his fourth fifty in five games. Singh chips in again, giving an insight into the teenager's brain.

"You see that shot? That's what sets him apart," he says. "Any other batsman and he would've gone for the pull. But Jaiswal knows that's not the right option when there's no run-rate pressure."

The reason Singh can analyse Jaiswal so well is because they've stayed under the same roof for five years now. Once upon a time, Jaiswal would live in the tents of Azad Maidan in Mumbai while beginning his cricketing journey, selling pani-puris, a street snack, after practice to stay financially afloat in India's most expensive city. But since Singh opened his home's doors for Jaiswal, they have practiced cricket in the daytime and chatted about everything else in the evenings.

"We have a rule at home. Every evening, he gives me a massage and tells me how his day went," Singh says. "Even if I forget to ask him for a massage, he will come to me. Because he's not had much of a childhood, he can get easily lured into things that teenagers do these days. So we discuss every aspect of his life. Everyday. But he is this headstrong because I've never given him anything on a platter. Even on the IPL auction day, I sent him to shop for groceries.

Yashasvi Jaiswal hits into the leg side Getty Images

"Once in a generation can someone become a legend. Jaiswal has that in him, which is why it's so important to stay grounded. There are so many players who have played for India and done well. But legends don't come by every day. That's what I have tried to drill into him. He has now come to understand what all he can achieve if he keeps his head in the right place.

"This one time, he was the Player of the Series in a local tournament. He got a INR 10,000 voucher. He said he wanted to buy a cricket helmet, so I gave him permission to buy one.

"When he came back, he said, 'I've spent INR 3000 extra, can you give me that money please?' That was the first time I got angry at him. I snatched the helmet from him and said, '13000 for a helmet? That's ridiculous. You will wear this when you really deserve it.'

"I put the helmet on top of his almirah after that. So that he could see it every day. The day he made his Ranji debut, I personally handed that helmet over to him. That's the day I realised that whatever goal you give Jaiswal, he will fulfil it."

Singh, who was also Prithvi Shaw's coach from 2015 to 2018, says that he feels blessed to have shaped two cricketers who are destined for greatness. At one time, Singh - from Gorakhpur in Uttar Pradesh - had dreams of being an India cricketer. But knee injuries dashed his hopes and so he chose to be a coach. He has recently given permission for a movie to be based on his life story. It's title is apt: Second Chance.

As Jaiswal reaches his nineties, I probe whether the now-successful Jaiswal - with an IPL contract at hand - has ever given him a gift, Singh's smile widens.

"You see his jersey number? It's 23 because that's my birth date," Singh says. "What more can I ask for?

"Before my daughter was born, he was my only child. Now he's an elder brother to my girl. Even my girl has proven lucky for him. The day she was born, December 6, 2017, he struck the double-hundred for Mumbai Under-19.

"He is so mature that when I said I'll give him a car for being the highest run-scorer, he said he doesn't want a new one. He wants to take my old Brezza so that I buy myself a new one."

A few moments later, Jaiswal reaches his hundred by slog-sweeping the Pakistan spinner Aamir Ali over deep midwicket. He raises his arms, looked upwards and says a silent prayer. Singh then says, "I think I'll reveal it to him now. That I'm here."