US stocks opened the fourth quarter on a weak note, with major indices slipping into negative territory. The S&P 500 declined 0.3%, the Nasdaq fell 0.2%, and the Dow Jones lost 245 points, erasing earlier gains as rising Treasury yields and another uptick in oil prices pressured sentiment. At the same time, the ISM Manufacturing PMI indicated a sharp increase in manufacturing prices, even as the overall slowdown in factory activity moderated. Sector performance was mixed: materials and real estate lagged the most, while energy shares outperformed.