Showtime turned a nifty ratings trick Monday, with new half-hour “Secret Diary of a Call Girl” premiering to record numbers.

“Call Girl” attracted 949,000 paying customers in its first run Monday, outranking every other series premiere in the three decade-plus history of Showtime. The previous record holder at the network was “The L Word,” which drew 936,000 viewers when it bowed.

The strong tune-in for “Call Girl” represents the latest triumph for Bob Greenblatt, the Showtime entertainment president who has launched hits such as “Dexter,” “The Tudors” and “Californication.”

It’s also a victory for former HBO chief Chris Albrecht. Now at IMG, Mr. Albrecht was responsible for selling “Call Girl”—an already-produced British series from IMG and Tiger Aspect—to Showtime.

“Call Girl” was given a big leg up by its lead-in, the fourth-season premiere of established Showtime smash “Weeds.” The latter series attracted 1.35 million viewers in its 10 p.m. run Monday, a stunning 65 percent rise over the show’s third-season premiere. It was also the single highest-rated telecast on Showtime since 2004, when Nielsen began reporting ratings for individual Showtime channels.

Showtime has already ordered a second season of “Call Girl.”

Updated: Premiere day. June 18, 12:59 a.m.