NEW YORK (MarketWatch) — U.S. stocks opened lower on Monday as economic data from China pointing to a continued slowdown, as well as concerns over Greece, prompted investors to pile into havens. Government bonds and gold attracted buyers, while global equities sold off. The S&P 500 SPX, -0.31% opened 5 points, or 0.2%, lower at 2,050. The Dow Jones Industrial Average DJIA, -0.44% slumped 80 points, or 0.4%, to 17,745. The Nasdaq Composite COMP, -0.36% began the day down 15 points, or 0.3%, at 4,730.