LONDON — Savile Row tends to be quiet in late August, as the financiers, oligarchs and occasional rock stars who patronize the street’s bespoke tailors are on vacation. But there was plenty of commotion at No. 40, where sartorial traditions were being gently upended and new ones were being forged.

Inside the airy space were the usual accouterments of luxury British men’s wear: swatch books from Holland and Sherry, David Bowie on the stereo. But the designs on offer were far from standard: a bomber jacket in off-white crochet; track pants in a brown houndstooth wool; and a blouson jacket with tiny Champion logos stitched together.

“We are quite rebellious, but very respectful to the craft that’s gone before us and the history of the street,” said Rav Matharu, 40, a former soccer player who started the Clothsurgeon in his London apartment a decade ago, and now counts the actor Riz Ahmed and soccer player Marcus Rashford among his clients.

The tradition of fine tailoring on Savile Row runs back to the turn of the 19th century, and Mr. Matharu is eager to continue it, taking up to 25 measurements to create custom patterns and making all of his clothes within the boundaries of London.

“I think that’s very important to keep that narrative going,” he added, “but innovating in terms of offering and silhouettes and fabrications.”

When the store opened in early August, it was the culmination of Mr. Matharu’s vision that luxury joggers can be made with the same attention to detail as a pair of gray flannel trousers. It is also the first shop on the Row to offer made-to-order streetwear, and the first to be owned and operated by a South Asian designer.

British style arbiters have taken notice. “Some might see the Clothsurgeon’s arrival as disruptive,” said Aleks Cvetkovic, a contributing lifestyle editor at the Financial Times. “Savile Row is a British institution with a long history of reinventing itself.”

On that Wednesday morning, Mr. Matharu was seated quietly behind a midcentury rosewood table, sketching a bomber jacket. He was dressed in his own creations: a black, robe-like jacket paired with baggy, gray tweed trousers and chunky white sneakers.

The jacket had no buttons, collars or lapels, but “there is a sleeve roll in there,” Mr. Matharu said in a nasal, Yorkshire accent. He pinched the shoulder to check its construction. “Very softly tailored, it’s just easy.”

Mr. Matharu never set out to be a fashion designer. The son of Indian immigrants whose father owned a corner shop in Leeds, he was a gifted athlete who overcame racist taunts and signed with his hometown team, Leeds United, at 17. But by 20, Mr. Matharu said that he had “lost my love for the game” and quit. He gave his mother “a chunk of change” and spent the rest on clothes and clubbing. When the money ran out, he had to find work.

Unsure of what to do next, Mr. Matharu got a job on the shop floor at the local Size?, a British sneaker chain. “I was lost,” he said. “People were coming in thinking I was shopping there.” But it became an education in the fundamentals of the fashion business.

After years of dithering, he enrolled in the Leeds Art University fashion program in 2006. He was 24 and arrived “not being able to sew at all, not being able to cut straight lines even,” Mr. Matharu said. He was determined, however, coming into the studio in the mornings with the cleaning staff and leaving only when they turned the lights off.

To cut precise lines, he began using a scalpel, “almost like drawing on the fabric,” Mr. Matharu said. A friend described him as “like a surgeon.” Thus the name of his brand was born.

“I remember his senior collection being quite outstanding,” said Nicola Knight, fashion course leader at Leeds. “Very of the moment, influenced by a mixture of music genres, culture and sport,” she said. “Even then, he seemed to have his fingers on the pulse.”

After graduating, Mr. Matharu moved to London in 2009 where he couch-surfed and kept himself afloat by selling off his prized sneaker collection, until he found a design job at House of Billiam, a now-defunct brand that made custom streetwear. It not only taught him about the bespoke tailoring business, but showed him the potential for high-end streetwear, just as brands like Off-White were blurring the line between streetwear and luxury. A few years later, Mr. Matharu set out on his own.

“I think it was the best thing,” said his wife, Parv Matharu, 39, who left a career in corporate real estate to run the company’s operations.

Money was tight in the early days and Mr. Matharu had to fit clients in the hallway of the couple’s London apartment. Early clients included the rapper ASAP Rocky, whom he met at the House of Billiam studio. Other musicians soon came knocking, including Kendrick Lamar, Nas and Santan Dave — drawn by the brand’s clever remixes of streetwear staples, cut with wit and precision.

After Mr. Matharu showed up to a Nike event in 2014 in a suit constructed from old Nike sweatpants, brands like Champion and Coca-Cola reached out for collaborations. Clothsurgeon has also collaborated with Harrods, Mr. Porter and Selfridges on small collections.

“When Rav pivoted to focus on remade and bespoke items for private clients, V.I.P.s and special orders, I thought at the time, ‘This is a modern approach to made-to-measure and Saville Row,’” said Jack Cassidy, the former men’s wear buyer and now accessories director at Selfridges.

There is hope that the Clothsurgeon will help breathe new life into a fabled but sleepy street that was hit hard by the pandemic. The Pollen Real Estate Trust, which owns and rents out the shops on Savile Row, had accepted the Matharus’ pitch in part because of their ability to bring “a new audience to the street,” said Julian Stocks, the property director of the trust.

The Matharus are aware of the scrutiny they face in representing so many “firsts” in this tony stretch of central London. “It’s a historic moment,” Ms. Matharu said. “It’s iconic, but actually it’s just made the bar even higher.”

In the early afternoon, two young South Asian men dressed in loose black ensembles tentatively entered the shop. “I’ve been following you for a while now,” said Nakaash Hussein, 31, a filmmaker from Nottingham who came to Mayfair to check out the shop. Scanning the racks, he was drawn to a varsity jacket made from a patchwork of Supreme blanket scraps (1,850 British pounds or a little over $2,100). “It’s Supreme and not Supreme,” Mr. Hussein said.

“And you don’t have to queue for it,” Mr. Matharu added.

An older English gentleman dressed in a white shirt and orange trousers poked his head through the door and inquired whether the shop was open. He described himself as “an occasional purchaser of goods” who has lived on Savile Row for 65 years. The man eyed the merchandise, running his hand approvingly over a red linen coat.

“Girls’ or men’s?” he asked in an accent as crisp as a 100 pound note.

“It’s men’s,” Mr. Matharu replied. “We can make it to your specifications.”

The old man liked the color, but when he saw the price tag (925 British pounds or about $1,080), he returned the jacket to the rack. “Who owns this place?”

“We do,” Mr. Matharu said.