It was the first Sunday this year that the two shows went head to head, as Strictly aired its first results show.
The pre-recorded episode between 7:15PM and 9PM averaged 8.5 million, 700,000 down on Saturday's live performance show but up 300,000 viewers on last year's equivalent results episode.
A peak audience of 9.3 million were watching when who left Strictly Come Dancing first was revealed.
The X Factor meanwhile kicked off its second bootcamp episode halfway through Strictly, running between 7:30PM and 9PM. The episode averaged 5.1 million viewers.
It was up slightly (100,000 viewers) on Sunday's show but down a million on last week to give the series its lowest Sunday rating yet. Last year's Sunday bootcamp show had 6.8 million viewers.
Strictly and X Factor will clash again both next Saturday and Sunday night. On Saturday, Strictly runs 6:35PM - 8:40PM while X Factor airs 8:15PM - 9:45PM. On the Sunday, Strictly's results air 7:15PM - 8PM while the start of X Factor's Six Chair Challenge airs 7:30PM - 9PM.
Elsewhere in last night's viewing figures, in the 9PM slot, Victoria took another hit as it dropped further from its series high of 4.9 million viewers down to 4.2 million, falling 100,000 viewers week-on-week.
It lost out to new BBC One drama series The Last Post, which had 4.7 million viewers in the same slot.
Earlier on BBC One, Antiques Roadshow was the most watched show of the day across all channels after Strictly with 5.9 million viewers.