The X Factor's launch show saw a fall of 800,000 viewers from last year's first episode and has received the lowest viewing figures since 2005, overnight data has revealed.
The return of ITV's talent-hunting programme was viewed by 6.8 million people on Saturday night.
This represented a 34% audience share, compared with the 2015 launch show which had initial overnight figures of 7.6 million and an audience share of 39%.
X Factor's second series in 2005 premiered with 6.72 million viewers, meaning this year's effort got off to a bumpy start with its lowest audience in 10 years.
However, the new series' debut had a peak audience of 7.5 million, while last year's launch peaked at 7.9 million, leaving just a 400,000 discrepancy.
The drop in numbers comes despite show boss Simon Cowell bringing back old favourites Louis Walsh, Sharon Osbourne and Nicole Scherzinger to the judging panel, and reinstating long-running host Dermot O'Leary after a year away.
Last year, The X Factor's first instalment suffered a two million drop in figures from the previous year: in 2014 an average of 8.9 million people watched the show on the same weekend despite Simon's hopes that the revamped format and judging panel would draw in more viewers.
The 2015 line-up included Simon, returning judge Cheryl Fernandez-Versini and newcomers Rita Ora and Nick Grimshaw - as well as presenting double-act Caroline Flack and Olly Murs.
Numbers for the first episode of the current series of The X Factor are set to rise as consolidated figures will be calculated for TV viewers watching on catch-up and other services.
Spin-off show The Xtra Factor Live, which has been given a make-over and is now being broadcast live from the start of the series, was watched by 809,000 viewers with an audience peak of 942,000.
The Rylan Clark-Neal and Matt Edmondson-fronted companion show was the second most-watched digital programme of the day behind the Hull City v Manchester United match on BT Sport, which averaged 827,000 viewers.
The X Factor's launch show still managed to pull in more viewers than the BBC's 30th anniversary episode of Casualty, which was the channel's most-watched programme on Saturday night with 5.1 million viewers and 26% of the audience share.
Overall feedback from the first show of the 13th series of Simon's singing competition has been positive.
Fans and critics praised the returning judging panel and Dermot, as well as the intimate room auditions, which had been scrapped in previous years for live auditions.
The series will face a fresh battle in the ratings when BBC's rival show Strictly Come Dancing kicks off with its launch show on September 3.