(Bloomberg)—U.K. web-only fashion retailer ASOS PLC’s push to offer domestic shoppers services such as a program that allows shoppers to try items on before they buy them and more robust delivery options helped boost the retailer’s U.K. sales 23.3% in the final four months of 2017. The retailer’s overall sales rose 30.5%.

“Our customer proposition was further enhanced in the U.K. with the launch of Try Before You Buy and ASOS Instant, our same day delivery proposition,” says CEO Nick Beighton.

The U.K.’s largest online-only fashion retailer’s gains largely came at the expense of store-based rivals.

“ASOS is enjoying the kind of sales growth that traditional retailers would give their eye teeth for,” said Laith Khalaf, senior analyst at Hargreaves Lansdown.

The growth at ASOS, which targets fashion-conscious twenty-somethings, is part of an accelerating shift online that’s hurting U.K. bricks-and-mortar retailers and their billionaire owners. Philip Green’s retail chains, including TopShop, recently requested price cuts from suppliers, citing the increased cost of doing business online. Meanwhile dwindling sales at New Look Retail Group Ltd., part-owned by South Africa’s Christo Wiese, has prompted the company to reassure investors that it has adequate liquidity.

While things are tough for Britain’s town-center retailers, competition is heating up online, too. Boohoo.com PLC doubled its sales in the 10 months to Dec. 31 and Amazon.com Inc. has made the fashion market a priority. To insulate itself, ASOS has introduced same-day delivery and a service that allows shoppers to return unwanted garments free of charge. That spending is driving sales growth, but restricting profits.

ASOS, No. 167 in the Internet Retailer Top 1000, has emerged as one of the few winners of a U.K. holiday shopping season characterized by subdued spending. Department-store chains Debenhams Plc and House of Fraser struggled, while grocers Tesco PLC and J Sainsbury PLC announced this week that thousands of management roles would be scrapped amid a drive to slash costs.

For the final four months of  2017, ASOS reported:

• U.K. retail sales of 300.9 million pounds ($400.9 million), up 23.3% from 244 million pounds ($349.0 million).
• U.S. retail sales of 102.4 million pounds ($146.47 million), up 23.8% from 82.7 million pounds ($118.3 million).
• Total retail sales of 790.4 million pounds ($1.13 billion), up 30.5% from 605.7 million pounds ($866.4 million).
• Total revenue of 808.4 million pounds ($1.16 billion), up from 621.3 million pounds ($888.7 million).

Internet Retailer featured ASOS’ try before you buy and fulfillment options in Internet Retailer’s Hot 100 issue. To read about other innovative online retailers, click here to download the free issue of the Hot 100.