Mobile edged desktop 47.4 million to 46.1 million in unique visitors to ESPN in September, dealing the desktop site its first loss to long-time underdog mobile.

It's a milestone already reached by Buzzfeed. BBC News saw majority mobile traffic for two days in July. And LinkedIn expects to get there next year.

Unique visitors isn't a perfect metric for readership, and ESPN users still spent more time overall on the desktop site than on mobile. But the fact that the number of visitors to ESPN's apps and mobile website now surpasses visitors to the desktop site helps validate the company's belief in mobile, said Rob King, ESPN’s senior vice president for content, digital & print media, via phone.

Over the last three years, King said, ESPN observed mobile web traffic outpacing traffic to the desktop site on Sundays during the NFL season as football fans checked fantasy numbers and game scores. But mobile-friendly video and stories throughout the day show ESPN isn't just focusing on supplementing live action, said King, who is a member of Poynter's national advisory board:

“We’re trying to get our fans to have the experiences they want, whether it’s a second screen while an event is going on, or whether it’s your primary screen or your only screen,” he said.