NEW YORK (MarketWatch) — U.S. stocks opened lower on Friday and were on track to end January with biggest monthly losses in a year. The main indexes were to on track to record a weekly loss. Investors flocked into havens such as Treasurys and sold off equities after government data showed economy slowed down in the fourth quarter by more than expected. The S&P 500 SPX, -0.29% opened down 9 points, or 0.5%, at 2,012. The Dow Jones Industrial Average DJIA, -0.18% fell 37 points, or 0.3%, to 17,280. The Nasdaq Composite COMP, +0.05% outperformed other indexes and turned higher shortly after the open, adding 9 points, or 0.2%, to 4,692.