By Anora Mahmudova, MarketWatch

NEW YORK (MarketWatch) -- The U.S. stock market opened with deep losses on Friday, as disappointing earnings and renewed fears over deflation in the euro zone prompted heavy selling on Wall Street.

The main indexes are on track to finish the week lower and record their steepest monthly decline since May 2012, as recent earnings news has been lackluster, while fears over emerging markets have sent many investors for cover.

Investors found no solace from U.S. consumer spending data, which showed Americans spent more in December, but their incomes stagnated.

The S&P 500 (SPX) opened 17 points, or 1%, lower at 1,777.11, and was set to record its third weekly decline in a row. The Dow Jones Industrial Average (DJI) began the session with a triple-digit loss, falling 187 points, or 1.2%, to 15,666.886. The blue-chip index is headed for the second straight week of losses.

The Nasdaq Composite (RIXF) opened down 34 points, or 0.9%, at 4,088.18. The tech-heavy index is set to register second straight week of declines. Follow our stock market live blog.

Stocks endured heavy selling in most of the sessions this week, as sharp drops in emerging-markets currencies prompted nervous investors to flee riskier assets including stocks and lock in profits from a spectacular year.

A batch of disappointing earnings before Friday's opening bell weighed on stocks.

Shares of Mattel(MAT) slid more than 10% after the toy maker reported a surprise fall in fourth-quarter sales due to sharp declines in core brands such as Barbie and Fisher-Price.

Wal-Mart Stores Inc (WMT) shares dropped 1.4% after the world's largest retailer cut its fourth-quarter earnings forecast. Wal-Mart warned the sales impact from the reduction in the U.S. government food stamps was greater than expected.

Amazon.com(AMZN) skidded 7.3% after sales came in just shy of estimates in its fourth-quarter earnings report released after the close on Thursday.

Chevron (CVX) shares slid 3.7% as the oil company reported lower profit and revenues than expected.

MasterCard Inc. (MA) shares slid 6.3% after the credit-card company missed Wall Street's expectations for its fourth-quarter profits.

One of the bright spots in the market was Zynga(ZNGA). Shares surged 20% after the games maker said it would cut its head count and buy NaturalMotion, a mobile videogame company, as it announced results late Thursday.

In economic news, data were fairly mixed. Consumer spending rose sharply in December for the second month in a row, but Americans had to dip into their savings to pay for their purchases. The incomes of Americans, however, were unchanged in December and they fell after adjusting for taxes and inflation. Economists polled by MarketWatch had forecast a smaller gain in spending but a slight rise in income.

Consumer sentiment, however, declined in January, as weak jobs growth continuing to weigh on consumers, according to Friday reports on a gauge from the University of Michigan and Thomson Reuters.

The Chicago PMI fell in January to a still-strong 59.6 from 60.8 in December, but employment weakened for the second straight month. Economists polled by MarketWatch had expected the index, formally known the Chicago business barometer, to decline to 59.8. Readings above 50.0 indicate expansion.

In other markets, 10-year Treasurys extended a rally, oil fell while gold inched higher and the dollar held on to recent gains. European stocks fell. In Asia, Japanese stocks eased.

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