The post-holiday slump of January isn’t usually a good time for an auspicious Broadway debut. But that didn’t stop “How to Succeed in Business Without Really Trying” from logging a stellar first week for the show’s new topliner, Darren Criss.

“How to Succeed” raked in $1,386,065, and those involved in the show say sales look poised to remain on that level for the next couple of weeks. B.O. isn’t fueled only by Criss’ avid fanbase, amassed from his work as an actor on “Glee” and as a co-creator of cult-fave homemade tuners including “A Very Potter Musical.” There’s also a sense of urgency for Rialto ticket buyers since Criss will stay in the show for a total of only three weeks before heading back to work on the Fox skein.

Next up for “How to Succeed” is a stint from another young-skewing star, Nick Jonas, though it seems unlikely there’ll be the same sort of instant frenzy given that Jonas will stick with the show for six months, allowing fans more time to catch a perf.

Tuner “Porgy and Bess” also got some January encouragement, rising a bit to $862,527. So far, show has steadily gained B.O. momentum throughout its preview period in advance of its opening Thursday.

“Porgy” was one of very few shows last week to uptick, not least because so many productions had played a sales-boosting ninth perf the previous sesh. Also up was “An Evening With Patti LuPone and Mandy Patinkin” ($539,026 for seven shows), on the rise in its final full week prior to its Friday closing.

Turns out, though, that there was enough holiday runoff to fuel million-plus sales at no fewer than eight shows (with “War Horse,” at $999,530, just missing the mark). At the top of the charts, “The Lion King” began the year in the No. 1 slot, edging out “Wicked” ($1,850,216) and “Spider-Man: Turn Off the Dark” ($1,721,734).

Meanwhile, the last week of 3-year-old “Billy Elliot” ($1,118,453) helped keep numbers high, and there were enough family auds in town to keep “Mary Poppins” ($1,046,746) in the millionaires’ club as well.

Otherwise, a number of shows started to feel the downward pull of winter. Among the fall’s offerings, unenthusiastically received revival “On a Clear Day You Can See Forever” ($584,711) slipped discouragingly while play “Chinglish” ($197,148) dropped below the $200,000 mark.

Overall Broadway cume deflated by $13.7 million to land at about $24 million for 31 shows on the boards. Attendance was 250,021 vs. 230,000 for 27 shows during the same sesh last year.

Along with “Billy Elliot,” last week saw the demise of the short-lived “Lysistrata Jones” ($254,776), which never pep-rallied sufficient biz to stay on the boards. Stepping into the fray was “Wit” ($121,813), playing the first five previews of a Manhattan Theater Club revival starring Cynthia Nixon.