Investors shrugged off strong quarterly sales and earnings and shares fell 6.2 percent to $71.2. They have risen almost 11 percent since the start of the year.

"The quarter was not pristine. Online sales growth decelerated meaningfully," said Jason Benowitz, analyst and senior portfolio manager at The Roosevelt Investment Group.

Best Buy did not update its full-year financial outlook, which could have also led Wall Street to assume a fairly steep deceleration in growth, Benowitz said.

The company reiterated its fiscal outlook provided in March.

CEO Hubert Joly said there was nothing to read into the company not updating its outlook as the retailer gave a wide range in its forecast this year.

"We just felt like there's so much of the year still in front of us," he said. "We are trending towards the higher end of our revenue range."

Domestic online comparable sales growth slowed to 12 percent, compared to 22.5 percent growth a year ago.

Chief Financial Officer Corie Barry said on a call with investors first-quarter online sales last fiscal year had benefited from product launches such as the Nintendo Switch and the Samsung S8, and the company gained online market share this quarter.

Joly said the distinction between online sales and stores sales is getting blurred, given half of the retailer's online orders are being shipped from or picked up in-store. "At some point in the future, reporting online sales separately may or may not make sense," he said.

Overall sales growth was aided by strong consumer demand and better product innovation. Demand for mobile phones, appliances, and computing drove comparable sales growth.

Sales at established stores rose 7.1 percent in the first quarter ended May 5, beating analysts' average expectation for a 2.9-percent increase, according to Consensus Metrix. The growth, the retailer's largest since fiscal 2005, benefited from an easier comparison to a relatively soft period a year ago.

Despite the slowdown in e-commerce sales during this quarter the company's turnaround has been strong. Best Buy has weathered the encroachment of Amazon.com Inc better than most retailers. It posted its best holiday quarter performance last year since 2003.

Best Buy has about 15 percent of the U.S. consumer electronics market. Along with Amazon, the two retailers have about 25 percent market share, leaving room to grow, Joly told Reuters in March.

The company's investments in price-matching, faster delivery, improving the search function on its website and better customer service have weighed on profitability.

Net income rose to $208 million (£155.77 million), or 72 cents per share, in the quarter, from $188 million, or 60 cents per share, a year earlier.

Excluding items, earnings were 82 cents per share. Analysts had expected 74 cents, according to Thomson Reuters I/B/E/S.

The company's revenue rose to $9.10 billion, beating estimates of $8.74 billion.

(Reporting by Nandita Bose in New York, Additional reporting by Uday Sampath Kumar in Bengaluru; Editing by Nick Zieminski)

By Nandita Bose