Shares of Alibaba.com, the Chinese B2B marketplace, nearly tripled in their Hong Kong debut, closing at HK$39.50 (US$5.09), after its IPO priced at HK $13.50 (US$1.74). The steep rise was easy to see coming, considering the groundswell of enthusiasm for the company preceding the IPO. The company now sports a $25.7 billion market cap, which brings it close with Yahoo (NSDQ: YHOO) Japan as the largest internet company in Asia, according to Bloomberg.

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As for what this means to shareholder Yahoo, Eric Savitz runs the math: “So, let’s see. Alibaba Group holds a 75% stake in Alibaba.com, which is worth $17.4 billion. Yahoo owns 39% of Alibaba Group, which puts the value of their share at $6.8 billion. The direct-owned 1.2% stake is worth about $278 million. That puts the total value of Yahoo’s interest in Alibaba.com at north of $7 billion. That’s about 16.7% of Yahoo’s current $42 billion valuation.”

Update: The news isn’t doing much for shares of Yahoo, which are off more than 4 percent today. Alibaba.com’s share price may already have been baked in to Yahoo, coupled with fears that the price is unsustainable. Also weighing on the company’s shares is CEO Jerry Yang’s appearance on Capitol Hill, defending the company’s handling of Chinese censorship probe.