The growth engines of Amazon.com Inc. and Alphabet Inc., the world's largest internet companies, sputtered last quarter, and after weeks of stock market jitters, investors were in no mood to give them a pass.

Amazon, the biggest online retailer, on Thursday reported a second consecutive quarter of sales that fell short of estimates — the first back-to-back revenue miss in almost four years. The company also gave a disappointing revenue and profit forecast for the busy holiday period, sending shares down as much as 9.4 percent in extended trading. Even its highly profitable cloud-computing business, Amazon Web Services, didn't grow as fast as it had in the previous three months.

Alphabet's third-quarter sales missed analysts' expectations, and revenue growth from its main Google sites, including search and YouTube, came in at 22 percent, slower than the prior period. Shares of the world's largest digital advertiser dropped 3.9 percent after the results were announced.