The first two games of the NBA championship series between the Boston Celtics and Los Angeles Lakers on ABC averaged nearly 15 million viewers, making them the most-watched prime-time programs on broadcast television last week, the Nielsen Co. said. It was the strongest opening for the NBA championship since the Lakers took on the Detroit Pistons in 1994, and up 10 percent over last year's championship.

Meanwhile, three games of the Stanley Cup hockey finals matching the Chicago Blackhawks with the Philadelphia Flyers on NBC were seen by 14 percent more people than the comparable three games last year.

Ratings for major sports events have been strong this year, including the record set for the most-watched Super Bowl. TV executives think it's no coincidence the increases coincide with Americans' rapid adoption of high-def television, popular with sports fans.

An estimated 52 percent of U.S. homes had HDTVs and were actively using them, according to a Nielsen study done in April. That compares with 33 percent a year earlier and 17 percent in 2008, Nielsen said.

1 NBA Finals Game 2 (ABC)

2 NBA Finals Game 1 (ABC)

3 America's Got Talent, Tue. (NBC)

4 NCIS (CBS)

5 60 Minutes (CBS)

6 America's Got Talent, Wed. (NBC)

7 Two and a Half Men (CBS)

8 The Big Bang Theory (CBS)

9 The Mentalist (CBS)

10 NCIS: Los Angeles (CBS)

11 Glee (Fox)

12 So You Think You Can Dance , Thu. (Fox)

13 CSI: NY (CBS)

14 Wipeout (ABC)

15 Criminal Minds (CBS)

16 CSI: Miami (CBS)

17 The Bachelorette (ABC)

18 CSI: Crime Scene Investigation (CBS)

19 So You Think You Can Dance, Wed. (Fox)

20 20/20 (ABC)