Days before third quarter earnings season began on Tuesday with Alcoa’s (NYSE:AA) earnings report, many analysts were optimistic because expectations have been set so low.

Standard and Poor’s tallied that the most recent earnings estimates for the S&P 500 Index is for earnings to grow 13 percent from a year ago, which is 3 percent lower than the July 27 estimate.

Ahead of Alcoa’s earnings report, U.S. stocks ended mixed on Tuesday, with earnings optimism partially overcoming worries over Slovakia’s approval of the proposed European Financial Stability Facility (ESFS) expansion.

The S&P 500 Index rose 0.05 percent, the Dow Jones Industrial Average fell 0.15 percent, and the Nasdaq Composite rallied 0.66 percent.

The market, in anticipation of good earnings from Alcoa, bid up the aluminum company’s shares by 2.08 percent in the regular session.

Alcoa’s actual results, however, disappointed the market.  It reported earnings of $0.15 per share, which exceeded last year’s $0.06 per share but fell short of expectations of $0.22 per share.

In after-hours trading, Alcoa shares plunged 4.66 percent.

The rude reality is that third quarter earnings will be disappointing, even against lowered expectations, said Patrick Moonen, a senior strategist at ING Investment Management.

Moonen, speaking to Bloomberg TV, cited global economic slowdown, currency volatility, and weak investor sentiment as factoring weighing on U.S. corporate earnings. 

Two sectors that may particularly disappoint are basic materials (on the global slowdown) and financials (on unfavorable industry conditions).

For example, analysts expect Goldman Sachs (NYSE:GS) to post a quarterly loss for only the second time in its history.