* Cyber Monday sales up 30.3 percent over 2011 - IBM * Amazon says its Kindle devices had biggest sales day ever * ChannelAdvisor says client sales growth stronger on eBay than Amazon By Alistair Barr Nov 27 (Reuters) - Internet sales jumped more than 30 percent on Cyber Monday, making it the biggest online shopping day ever, according to data released on Tuesday. Walmart.com, the online division of Walmart U.S., had its best sales day in history, a spokeswoman said. Cyber Monday also was a record day for sales of Amazon.com Inc's Kindle devices, the online retailer said, without specifying the number sold. Still, eBay Inc, operator of one of the largest online marketplaces, outperformed its arch rival Amazon.com over the crucial first five days of the holiday shopping season, according to one closely watched measure. Cyber Monday has been the biggest online shopping day in recent years, as workers return to offices and make holiday purchases on their computers. This year, the boom in smart phone and tablet adoption has added extra fuel to online shopping. Cyber Monday sales online jumped 30.3 percent from the same day last year, according to International Business Machines Corp , which analyzes transactions from 500 U.S. retailers. Mobile devices accounted for 18 percent of visits to retailer websites and 13 percent of sales on Cyber Monday. That was up 70 percent and 96 percent, respectively, compared with the same day last year, IBM reported. To that end, Walmart.com said Cyber Monday online traffic from Walmart's mobile apps jumped 280 percent versus a year ago. On Monday, when retailers offered big Cyber Monday online deals, web shopping peaked at 11:25 a.m. EST (1625 GMT), IBM said. That timing suggests shoppers continue to check out online offers while still at work, even though more people have high-speed Internet access at home than in previous years. AMAZON'S KINDLE DEAL Amazon.com cut the price of its 7-inch Kindle Fire tablet by $30 to $129 on Monday, and it was the company's most successful Cyber Monday deal ever, the retailer said. Nine of the top 10 best-selling products on Amazon.com have been Kindles, Kindle accessories and digital content since the company unveiled new devices on Sept. 6, it said. Worldwide sales of Kindle devices more than doubled during the Thanksgiving weekend from the 2011 period, Amazon said. "Demand for Kindle Fire is stronger than expected," said Chad Bartley, an analyst at Pacific Crest Securities. "This suggests Amazon is competing effectively against Apple and Google in the near term, and increased device ownership could drive sales of digital media and physical products over the long term." Bartley raised his estimate for fourth-quarter Kindle Fire unit sales to 8 million from 5.5 million and increased his forecast for Amazon's fourth-quarter revenue to $22.75 billion from $22.25 billion. Shares of Amazon closed down almost 0.1 percent at $243.40 on Nasdaq. Stock in Wal-Mart Stores Inc shed 0.6 percent to close at $69.50. A FIRST FOR EBAY Still, eBay sales may have outperformed Amazon during the early part of the holiday shopping season, according to ChannelAdvisor, which helps third-party merchants sell more via websites including eBay.com and Amazon.com. ChannelAdvisor data excludes sales specifically by Amazon, so the data does not capture Kindle device revenue and many other transactions. About 60 percent of Amazon's unit sales are generated by the company itself, while 40 percent come from third parties operating on its platform. ChannelAdvisor said client sales - sales generated by third-party merchants using the company's service - soared 55.2 percent on eBay.com on Cyber Monday from a year earlier. That was about five times faster than last year's growth. For the five-day period from Thanksgiving through Cyber Monday, which ChannelAdvisor calls the "Cyber Five," client sales on eBay.com rose 38.3 percent compared with the same days in 2011. ChannelAdvisor said client sales on Amazon.com jumped 42.4 percent on Cyber Monday compared with a year earlier. Over the "Cyber Five," client sales on Amazon.com rose 37.7 percent, the firm said. This is the first time since at least 2007 that client sales on eBay.com have grown faster than client sales via Amazon.com during the holiday season, according to Scot Wingo, chief executive of ChannelAdvisor. The firm started tracking this in 2007, he noted. EBay shares lost 0.5 percent to close at $51.15 on Tuesday. The stock rose almost 5 percent to a new multi-year high on Monday after ChannelAdvisor released its early Cyber Monday results. EBay's holiday advertising campaign, which included TV commercials, likely attracted more shoppers to its online marketplace, Wingo said. EBay was also "aggressive" with holiday promotions and gift guides, and the company's category-specific websites focused on things like fashion and electronics, were well integrated with the broader holiday promotions, unlike last year, Wingo explained. However, the main driver may have been mobile shopping, an area in which eBay and its payments division PayPal invested early and heavily, Wingo added. "With less than 10 percent of commerce coming from mobile devices and far higher levels ahead, we believe this trend will carry eBay Marketplace and PayPal for the next few years," Gil Luria, an analyst at Wedbush Securities, wrote in a note to investors on Tuesday.