According to Nielsen, the USA v Ghana World Cup match pulled a 2.6 rating and 3.819 million viewers on ESPN, making it the #7 Cable TV program for the week of June 19th. Not too shabby considering it was on between 7AM and 10AM on a weekday across the country. Via MultiChannel News:

"ESPN officials said the contest ranks as the fifth-highest-rated and second-most-viewed soccer match in the network’s history, trailing only the U.S.-Germany quarterfinal match in the 2002 World Cup, which drew a 4.4 household rating and 3.77 million homes."

The MultiChannel News article also contained some interesting average ratings info:

ESPN, which had aired 28 matches through June 22, posted a 1.0 household rating, 938,000 homes and 1.17 million viewers, respective gains of 67%, 94% and 82% relative to the same stage in the 2002 tourney.

For its part, ABC averaged a 2.5 household rating, 2.79 million homes and 3.74 million viewers during its first eight games through June 18. Those levels were 89%, 97% and 103% above the 2002 competition, when ABC had only presented three matches to that stage.

I should note that MultiChannel News said the US v Ghana match netted a 3.2 rating – not sure why they don’t match. MultiChannel News also had overall ratings information for Univision:

For 50 2006 World Cup matches through June 24, Univision averaged 1.44 million households and 2.17 million viewers, up 133% and 155%, respectively from the same span in 2002, when the World Cup was held in Korea and Japan and most of the matches aired live in overnight periods in the U.S. due to the time-zone differential from the Pacific Rim. [ed. matches aired often after midnight]

Compared with the 1998 World Cup in France — when the time zone differential to the East Coast in the United States was the same six hours as it is Germany — the 2006 World Cup was ahead 86% in households and 91% in viewers, according to Univision officials.

I wasn’t able to find a rating for the USA v Ghana match for Univision to get a combined US rating for the match. If you know it, please post in the comments! Sure, 15.71 million viewers watched Game 6 of the NBA finals – in prime time. But assuming that Univision pulled in 1.5 times the viewers that ESPN did (that’s the average ratio), that gives you 9.55 million viewers for the USA v Ghana match. In the early morning on a Thursday.

That’s damn impressive.
I’m done listening to "soccer will never be popular in the US". Talk to the hand.