U.S. stocks opened narrowly mixed on Monday to start the busiest week in the second-quarter earnings season. About a third of S&P 500 companies are due to report earnings this week, including eight Dow Jones Industrial Average components such as AT&T and Boeing. Dow component McDonald\'s Corp. reported disappointing earnings before Monday\'s opening bell. The fast food chain made net income of 1.40 billion U.S. dollars, or 1.38 dollars per share, on revenues of 7.08 billion dollars in the second quarter. The results were better than its year-ago numbers but missed analysts\' expectations of earning 1.40 dollars per share on revenues of 7.1 billion dollars. Shares of McDonald\'s sank 2.94 percent to trade at 97.32 dollars per share shortly after the opening bell, the biggest laggard of the Dow. Also reporting earnings on Monday are Texas Instruments and Netflix. Meanwhile, Apple\'s report due on Tuesday is expected to be a spotlight of the market. The mean earnings-per-share (EPS) estimate for Apple for the second quarter of 2013 is 7.33 dollars, relative to year-ago EPS of 9.32 dollars, said FactSet Senior Earnings Analyst John Butters in a note on Saturday. \"As a result of this expected EPS decrease and Apple\'s earnings weight in the index (the S&P 500), the company is the largest contributor to the earnings decline for the Information Technology sector for the second consecutive quarter,\" Butters said. According to Thomson Reuters data, roughly 20 percent of S&P 500 companies have reported second-quarter earnings, among which some 65.4 percent beat Wall Street earnings estimates and about a half surpassed revenue forecast. On the economic front, the National Association of Realtors will release U.S. existing home sales data for June. Analysts polled by Bloomberg expected June\'s existing home sales to rise to an annual rate of 5.27 million from 5.18 million in May. Shortly after the opening bell, the Dow Jones Industrial Average lost 12.65 points, or 0.08 percent, to 15,531.09 points. The S&P 500 added 1.10 points, or 0.07 percent, to 1,693.19 points. The Nasdaq Composite Index gained 9.09 points, or 0.25 percent, to 3,596.70 points.