They are both 14, but Lawrence is already 1.88m tall, dwarfing the 1.74m-tall Jack. They first met at the age of eight - not as partners but as rivals. They came across each other in two finals - one at a local novice tournament and the other at a year-end event.
Lawrence, now a Year 10 student at Renaissance College, won both hard-fought battles.
"The matches were both classics," he says. "Many years have passed since then, but I still remember even the scores."
So they started out as sworn enemies on the court. They would each try to tire the other out during long matches.
"We were not strong enough yet to have powerful shots. So my way to prevail was to be tough and consistent," Lawrence recalls. "I tried to play long balls to push my opponent to make errors. It worked on most players but not Jack. He is so tenacious and just didn't give in during a match."
Jack, a Form Three student at La Salle College, was likewise frustrated with Lawrence. "We always had close matches but I ended up making more errors and so he beat me in the end," he says.
Jack and Lawrence did not speak to each other much off the court. But their parents did. They saw the potential for a tennis duo. "Both of us were looking for a doubles partner," Jack says. "Our parents had a chit-chat by chance and they agreed to let us try partnering."
They were nine then - and they haven't looked back.
Lawrence's trademark single-handed backhand and Jack's aggressive net play make them a formidable pair. They have even overcome older opponents. They won the under-12 boys' doubles series competition during their very first tournament as partners. Last summer, they won gold for Hong Kong in the boys' doubles at the International Children's Games in Daegu, South Korea.
Jack says Lawrence gives him a sense of security on court. "I feel safe letting him play at the baseline while I stay near the net to play volleys. He's very reliable," he says.
Lawrence returns the compliment. "Jack has good volleys," he says. "We think alike on court. I know he is the best partner I could have."
The youngsters are widely seen as possible successors to the city's ace boys' doubles pair, Kevin Wong Chun-hun and Brian Yeung Pak-long, who are both in their final year at Diocesan Boys' School.
They agree. "We often joke that Jack is the 'Kevin' and I am the 'Brian' of our pair," Lawrence notes. "Just like them, we have good chemistry. I believe we have potential to be as good as they are."
The duo started playing in ITF Junior Circuit tournaments last year and may represent Hong Kong at this summer's Asian Youth Games in Nanjing .
"We often fly overseas together [for our singles games] so we can play together in the doubles," Jack says.
"It's always good to travel with him. The only thing I dislike is the possibility that I may need to face him in a singles match."