Brian O’Keefe:

The biggest company in the world has a chip on its shoulder right now—and that’s probably a good thing. Why? The ever-growing challenge from online retailers is pushing Walmart to be a much better operator in the digital world.

“For us, a big part of it is being paranoid,” said Walmart chairman Greg Penner on Thursday at the Fortune Global Forum in Guangzhou, China. “We’re at our best when we’ve got a competitor that’s really challenging us.”

If so, the mega-retailer is doubly blessed: It now has two mammoth online retailers targeting its core business.

For quite some time, Walmart, No. 1 on Fortune’s Global 500 list of the world’s largest companies with $486 billion in sales last year, has been working to adjust its strategy to reckon with the threat posed by