The season premiere of fan fave “Downton Abbey” scored solid numbers for PBS.

Sunday’s opener averaged 4.2 million viewers at 9 p.m. and doubled the network’s average prime-time viewership (2 million viewers), according to overnight data.

It was also up 18 percent over “Abbey’s” Season 1 premiere (Jan. 9, 2011).

In addition to over-the-air, Sunday’s episode was a hit in cyberspace, generating nearly 25,000 comments on the Internet, according to socialguide.com.

And, according to trendrr.tv — which compiles Twitter and Facebook mentions — “Downton Abbey” was “one of the most discussed broadcast programs” last Sunday.

The series, set against the backdrop of World War I, stars Maggie Smith, Elizabeth McGovern and Dan Stevens.