Aluminum producer Alcoa marked the unofficial start of earnings season Tuesday by posting sales that beat analyst expectations.

Alcoa (AA) is the first Dow component to report fourth-quarter results. The company posted earnings of six cents a share, in line with expectations, while sales were $5.9 billion, ahead of the predicted $5.6 billion.

Shares rose 2% in after-hours trading.

Alcoa's results are traditionally viewed as the start of earnings season, although most companies don't report until late January and early February, and the firm isn't seen as a bellwether for the broader market.

Overall, fourth-quarter earnings for S&P 500 companies are expected to rise 3.3% from the fourth quarter of 2011, according to S&P Capital IQ.

Excluding financial stocks, however, earnings are only expected to rise 0.5%, Dan Greenhaus, chief global strategist at BTIG, wrote in a research note Tuesday. He said these muted expectations were driven in significant part by the technology sector, where a number of firms have issued weak fourth-quarter guidance.