As noted, the first hour of RAW drew 2.833 million viewers, the second scored 2.717 million viewers and the final hour garnered 2.520 million viewers, an 11% drop from hour one. The third hour was the least watched hour - including holidays - since the show went to three hours (and likely since the mid-90s, however early ratings records for RAW only displayed the rating, not the viewership).
The show was up against the Monday Night Football season-opener double header, which averaged 12.96 million viewers for the first game and 10.252 million for the second. While it's easy to blame the lousy rating on Monday Night Football, Monday Night Football was actually down from last year. The Rams - 49ers game, which was head-to-head with the third hour RAW, was down 25% from last year and was the lowest rated "late-window" game since 2008.
Below is the audience for RAW against the Monday Night Football season-opener for every year since 2012, when the show went to three hours. The number in parenthesis indicates the increase or decline from the prior year. The fall from 2015 to 2016 was the largest yet:
2012: 4.136 million viewers
2013: 3.886 million viewers (-6%)
2014: 3.987 million viewers (+2.6%)
2015: 3.397 million viewers (-14.8%)
2016: 2.69 million viewers (-20.81%)