The opening night of action from the London Games performed nicely for NBC, coming in well ahead of the comparable night four years ago.

Nielsen estimates that the 8:30 to 11:30 p.m. coverage averaged an 18.0 overnight household rating/33 share — the best ever rating for the first night of competition for a non-U.S. Summer Games. By comparison, it ranked 8% better than Beijing in 2008 and 22% higher than the Athens Games in 2004.

NBC was expected to release more detailed viewership numbers later Sunday morning, but preliminary Nielsen estimates show the net’s primetime coverage averaging more than 27 million viewers. ABC, CBS and Fox combined to draw about 7 million on the night.

Four years ago in Beijing, the opening Saturday of the Games averaged 24.1 million viewers in primetime for NBC, though this average did not include the 8 p.m. half-hour. Using the same exclusion this time around would bump the nightly total up to nearly 29 million as viewership really picked up starting in the 9 p.m. half-hour.

The U.S. captured five medals on the opening day of action, including a gold for Ryan Lochte in a 400-meter individual medley battle of titans against Michael Phelps.

One night earlier, the four-hour Opening Ceremonies drew an average audience of 40.7 million viewers, according to Nielsen, making it the most-watched kickoff to the Summer Games on record. The tune-in was nearly 6 million larger than for Beijing in 2008 and bested the previous high, set by the Atlanta Games in 1996 (39.8 million), by nearly 1 million.

In household rating/share, Friday’s opener averaged a big 21.0/37, the best for a non-U.S. Summer Olympics ever, and the second best for a non-U.S. Games (summer of winter) in 36 years — since Innsbruck in February 1976 (23.2/37 on ABC).