Already the best-performing big-cap Internet stock, Amazon.com (AMZN - commentary - Cramer's Take) has just won itself more supporters.

Shares surged more than 18% early Wednesday after the online retailer blew away the Street's first-quarter earnings expectations and ratcheted up revenue guidance for the second quarter and full year. Piper Jaffray upgraded the stock to market perform from underperform, citing margin gains. That move came two days after Piper downgraded the stock, citing valuation concerns.

Those concerns weren't evident Wednesday. Shares of Amazon climbed $8.24 to $52.99.

The online retailer said net income more than doubled to $111 million, or 26 cents a share, from $51 million, or 12 cents a share, a year earlier. Amazon said its first-quarter effective tax rate fell to 23% from 47% a year earlier.

Sales jumped 32% to $3.02 billion.

Analysts surveyed by Thomson Financial had forecast Amazon to earn 15 cents on $2.92 billion in revenue.

For the second quarter, the company said it expects sales of between $2.7 billion and $2.85 billion; analysts were expecting $2.69 billion.

For the full year, the company said it expects sales of between $13.4 billion and $14 billion, above the current First Call consensus of $13.39 billion.

Amazon's closely watched operating margins came in at 4.8% for the first quarter, above the 4.6% it had reported a year ago. In its fourth quarter, Amazon reported operating margins of 4.9%.

Amazon's spending on technology and content, another metric causing apprehension in Wall Street, edged down year over year. The company reported that 6.2% of sales were invested in technology and content for the quarter, as compared with 6.4% for the same period a year earlier.