Simon Cowell’s X Factor spin-off launched with just under five million viewers.
Louis Walsh and Nicole Scherzinger joined the TV mogul as judges in The X Factor: Celebrity.
The first episode, on ITV, drew an average of 4.8 million viewers.
That is down on the 5.5 million who saw Dalton Harris win the X Factor in 2018, according to overnight ratings.
Saturday night’s programme – with journalist Martin Bashir, Love Island’s Wes Nelson and rugby player Ben Foden among those taking part – peaked with 5.3 million.
But the celebrity spin-off was the most watched show on ITV and won its 8.35pm time slot, the broadcaster said, with a 27.3% audience share.
ITV also said the show won the night among 16 to 34-year-old viewers.
But Strictly Come Dancing was the most watched show across all channels for the night.
It had an average of 8.5 million (a 45.6% audience share) and peaked with 9.1 million.
The Saturday night BBC One show is broadcast earlier than The X Factor: Celebrity, kicking off at 6.40pm.