July 12 (Reuters) - The S&P 500 opened at an all-time high on Monday, extending a record run from the previous session, with investors awaiting the start of the second-quarter earnings season and a batch of economic data. The Dow Jones Industrial Average fell 33.41 points, or 0.10%, at the open to 34,836.75. The S&P 500 opened higher by 2.86 points, or 0.07%, at 4,372.41, while the Nasdaq Composite gained 41.94 points, or 0.29%, to 14,743.86 at the opening bell. (Reporting by Shreyashi Sanyal in Bengalurul; Editing by Maju Samuel) Our Standards: The Thomson Reuters Trust Principles.