When Google (NASDAQ:GOOG) overtook eBay (NASDAQ:EBAY) earlier this year to become the Internet's most valuable stock, few figured that the search-engine king was preparing to take some more shots at the online auction house. Well, if a story first reported in Friday's Wall Street Journal holds up, Google is doing just that: It's reportedly getting ready to launch an online payment service -- its own version of PayPal -- later this year.

PayPal is a critical component of eBay's growth strategy. While eBay's stateside auction business slowed to a mere 20% top-line improvement this past quarter, PayPal came through with a 47% growth spurt. There are 71.6 million PayPal accounts out there, a number that compares favorably to the 60.5 million active accounts on eBay's namesake marketplace.

That's why eBay can't let PayPal fail, despite headier growth in its core auction business overseas.

Then again, one can argue that Google needs an answer to PayPal just as badly. A full 99% of the search star's revenue is tied to online advertising. Despite its lack of revenue stream diversification, it's doing a lot right within that niche to make investors rest more easily. But the company has a reputable connection with so many online users that it would be remiss not to branch out into web-based financial services.

This doesn't mean that PayPal's days as the king of pay are numbered. Established banking outfits like Citigroup (NYSE:C) and even Yahoo! (NASDAQ:YHOO) have tried -- and failed -- miserably. Even eBay couldn't topple PayPal when it hooked up with Wells Fargo (NYSE:WFC) to introduce Billpoint a few years back. That's why it eventually bit its lip and acquired PayPal three summers ago.

But won't Google's potential presence in online pay force PayPal to cut fees to remain competitive? And if so, won't that hurt eBay even if PayPal remains the top dog? Let's not rush to that conclusion. Despite cut-rate competition from the likes of Yahoo!, Amazon.com (NASDAQ:AMZN), and even Rule Breakers stock pick Overstock.com (NASDAQ:OSTK), eBay itself hasn't had to cut its auctioneering fees.

Then again, Google is special. Sure, the stock-picking graveyard is littered with the pompous souls muttering that "it's different this time," but, hey, it really is different this time.

Look beyond Google's search engine. Check out Google's mapping feature, or AdSense, or Froogle, or even its amazing aggregated news page. The company has a knack for successfully topping -- if not outright toppling -- the competition.

In the past, eBay has been able to acquire its headaches. Half.com? PayPal? Craigslist? Done, done, and partially done. Google is too big for eBay to buy. If this fight in pay does take place, man, is it going to be a good one.

Some other eBay-related links to check out as the company potentially braces for the Google onslaught:

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Longtime Fool contributor Rick Munarriz is a fan of both eBay and Google, but he will still splurge for ringside seats to see the two go at one another for a few rounds. He does not own shares in any of the companies mentioned in this story. The Fool has a disclosure policy. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early.