FXX scored solid ratings in primetime Thursday with its “The Simpsons” marathon, more than tripling the network’s usual audience and contributing to the nascent channel’s most-watched day ever.

According to Nielsen estimates, the six half-hours of “The Simpsons” averaged a 0.49 rating in adults 18-49 and 1.01 million viewers overall. The demo score was good enough for a fifth-place primetime finish for FXX — ahead of parent network FX as well as cable biggies including TNT and USA.

FXX also ranked No. 1 in basic cable primetime Thursday in men 18-34.

Last week in primetime, FXX averaged a 0.13 rating in adults 18-49 (165,000 in that age group) and 304,000 viewers overall. Also by way of comparison, the most recent original of the net’s “It’s Always Sunny in Philadelphia” averaged a 0.35 rating in the demo and 535,000 total viewers.

On a total-day basis, Thursday crushed FXX records, soaring 618% above its prior average in adults 18-49 (402,000 vs. 56,000) and 524% higher in total viewers (624,000 vs. 100,000).

All 552 “Simpsons” episodes will be airing in chronological order on FXX, which started the marathon earlier Thursday with the pilot episode from December 1989.

In primetime on Thursday, the top-rated “Simpsons” aired at 8:30 p.m., “Itchy & Scratchy & Marge,” averaging a 0.59 rating in 18-49 and 1.23 million total viewers. The early primetime peak is likely the result of increased cable comedy competition in the 9 o’clock hour, including “The Big Bang Theory” on TBS and current “Simpsons” Fox skedmate “Family Guy,” airing on Adult Swim.

During the 10 o’clock hour, “The Simpsons” averaged a 0.42 rating in adults 18-49 and 872,000 total viewers — beating out FX’s firstrun-comedy combo of “Married” (0.39 in 18-49, 678,000) and “You’re the Worst” (0.31, 555,000).