Apple briefly lost the title of world's most valuable company this week, as Alphabet (Google's parent company) overtook the Cupertino tech giant on a stock bounce the day after it released its quarterly earnings report late Monday.

Alphabet only held the title for a day, though, as Apple climbed back throughout the rest of the week. Here's why Alphabet and Apple are neck and neck.

Alphabet (Google) Beats Apple

On Tuesday, Alphabet's stock value climbed in trading by more than three percent, after the main revenue-generating division of the umbrella company (hint, it starts with a "G") propelled Alphabet to beat earnings expectations.

Alphabet posted earnings of $8.67 per share, when expectations were closer to $8.10, while total revenue growth shot to $21.3 billion over last year's $14.5 billion, beating the analysts' estimate around $16.9 billion.

After the company posted its stronger-than-expected Q4 earnings report on late Monday, shares in Alphabet shot up eight percent in after-hours trading, followed by the three percent rally on Tuesday. Put together, Alphabet's market capitalization surpassed Apple's by more than $10 billion at the end of trading, with Alphabet at more than $540 billion compared to Apple's drop to less than $530 billion, according to MarketWatch.

Alphabet Structured for Growth

Part of the trick for Alphabet's big, though temporary, victory over Apple this week was the difference in growth rates between the company, which can be traced in part to the very reason for Alphabet's existence: restructuring Google's vast array of projects to make more financial sense.

As The Guardian reported, in the past six months alone since Google created Alphabet to house all of Google's more ambitious projects and separate Google's core business from them, the company's market cap has risen by $200 billion.

Tellingly, the non-Google side of Alphabet posted a net loss on Monday, while Google's outstanding revenue growth pulled the company into beating earnings expectations. It helps that now Google's effective tax rate has dropped to 5 percent from 18 percent previously, as MarketWatch's earnings blog noted. And Monday's was Alphabet's first earnings report where it broke out Google from its "other bets."

While Google is a solid earnings machine, investors also do see many of Alphabet's "other bets" as a potential for future growth. Future technologies like autonomous cars, which are often called "Moonshots" by Google (until they become a reality), drive investors' optimism for break-out returns on investment, even if it's a long-term bet.

Apple's iPhone Slow-Down

Of course, it didn't help Apple that it famously posted the first deceleration in the growth of its iPhone revenue this quarter. Many investors see it changing from a high-growth tech stock to a healthy, but boringly stable value stock.

As far as growth potential -- especially in the mid-to-long term -- Apple doesn't seem to have as many ideas in the pipeline as Alphabet does.

Alphabet's Bounce Ends

Nevertheless, Apple took the title of world's most valuable public company on Wednesday, after a short selloff of Alphabet's stock following news that the head of search at Google was retiring. Alphabet lost seven percent of its stock price by Thursday, and its market capitalization cratered back below $500 billion.

The steady-but-boring Apple rose a couple percentage points at the same time, beating Alphabet to regain its title by more than $40 billion.

If you think that's the end of the neck-and-neck competition for "world's most valuable company," you're mistaken. It's likely that Alphabet and Apple will be effectively tied for that title, with each gaining the edge now and then, for a while.