MSNBC beat out Fox News last week in key ratings for first time in 17 years, topping its competitor in total viewers for the first time since 2000, according to a news release from MSNBC.

MSNBC averaged 1.56 million total viewers during the "sales day" (6 a.m. to 2 a.m.) between Dec. 17-21, making it the top cable news network in the key 25-54 age demographic.

Fox News averaged 1.54 million total viewers while CNN averaged 975,000.

In prime time (8 p.m. to 11 p.m.), MSNBC continued to lead Fox News and CNN in total viewers and among that key age group for the fourth week in a row.

MSNBC prime time last week averaged 2.58 million total viewers, compared to Fox's 2.24 million and CNN's 1.398 million. Of those viewers, 471,000 were between the ages of 25 and 54 for MSNBC. Fox saw 355,000 viewers in that demographic, while CNN saw 415,000 viewers.

The week's ratings marked a significant drop for Fox, which typically leads the pack.

The latest data means MSNBC could be on track to top Fox News in prime time for the month of December, according to MSNBC.

"The Rachel Maddow Show" finished the week as the top-rated program across all cable news networks, averaging 3.21 million total viewers by Dec. 21.

Sean Hannity's top-rated Fox show was off all of last week, which could have slowed Fox's viewership, a network spokesperson told The Hill. "Hannity" in October boasted an average total audience of 3.340 million viewers, making him the most-watched host in cable news in the third quarter, Forbes reported.

A Fox News spokesperson told The Hill that Fox News Channel is on track to beat out its competitors for the quarter and the year, having the highest-rated year ever in prime time.

- Updated at 9:59 p.m.