At the official close of trade, Alphabet was worth USD 530.1 billion based on its share value, compared to USD 534.7 billion for Apple, but shares in the Internet search colossus soared in after-hours trading to reach USD 791 shortly before 0400 GMT.
If those gains hold in official trading when the Nasdaq opens in New York City today, Alphabet would officially overtake Apple as the world's biggest company by market value.
Alphabet's reported quarterly profit rose five percent to USD 4.92 billion on the back of strong online advertising revenue, particularly from searches done by holiday season shoppers using smartphones or tablets.
People made purchases online when time allowed, with Google powering many of their searches and serving up related ads.
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Google ad revenue climbed globally, gaining on both mobile devices and desktop computers, according to Alphabet chief financial officer Ruth Porat.
The California-based Internet colossus said its revenue topped USD 21.3 billion in the final three months of last year.
Prime revenue drivers in Q4 were mobile search ads and ads on YouTube, where people watch "hundreds of millions" of hours of video daily.
The earnings report was the first in which recently formed parent corporation Alphabet separated money made by Google from what it calls "Other Bets" such as its work on self-driving cars or delivering Internet using high-altitude balloons.
The new structure under Alphabet is expected to offer more transparency for investors worried about Google investing in money-losing projects.
"Essentially, what they have now is a big advertising business and a venture capital business," Forrester analyst Frank Gillett said of the new earnings presentation.