For the past several weeks, NBC Olympics executives had insisted that despite all the problems leading up to Rio Summer Olympics, all indications pointed to viewers being more excited to watch the Games than ever before. But that's not what happened Friday night, as ratings for the opening ceremony dropped 28 percent from the 2012 Summer Games in London, according to metered-marked overnight ratings.

Even more alarming for the network, the 17.2 overnight rating reflects the lowest opening ceremony ratings since the Barcelona Olympics in 1992.

Meanwhile, viewers who did tune-in took to social media with two major complaints: NBC's decision to air and stream the ceremony on a one-hour delay, and what they saw as an excessive number of commercials during the ceremony. After last night's social media response, NBC Sports defended its ad load and tape delay decisions to Adweek.

NBC Sports said the overnight rating peaked at 19.0 from 10 p.m. to 10:15 p.m., when Team USA marched in, which was an hour earlier than during the London opening ceremony. Earlier this week, NBC Olympics executive producer Jim Bell denied reports that NBC tried to get the IOC to change the opening ceremony running order, moving the introduction of Team USA to the end to increase ratings for the full broadcast. "That story was false," he said.

Just before the games began, NBCUniversal announced that it had sold more than $1.2 billion in national ads for the Olympics, 75 percent of which accounted for advertising in NBC's prime-time coverage.

The network was certainly hoping for a higher rating, since it was optimistic that this could be the highest-rated Olympics ever.

This year, NBCUniversal guaranteed advertisers household live-plus-same-day household ratings "in the high teens" for NBC's prime-time coverage. The 2012 Olympics averaged a 17.5 household rating and 31.1 million total viewers in NBC prime time. (2014's Winter Games averaged a 12.3 household rating, with 21.4 million viewers.)

If the rest of NBC's Rio Olympics coverage also sees a ratings falloff from London, the company will have to offer advertisers make-goods later in the games, which will hamper its efforts to increase its $1.2 billion Olympics ad windfall.