The BBC One singing show attracted 36.5% of the audience share when its fifth episode of the series aired at 7.10pm.
In the same timeslot on ITV, Tom Daley's Splash! continued with 2.61m (11.87%), as Richard Whitehead and Towie's Dan Osborne made it through to next week's live final.
Back on BBC One, National Lottery: Who Dares Wins drew an audience of 5.38m (24.5%) at 8.35pm, while the latest episode of Casualty was watched by 5.31m (25.5%) at 9.25pm.
Over on BBC Two, 2.76m (12%) caught the channel's coverage of Sochi 2014 with Winter Olympics: Today at the Games at 7pm.
Torvill & Dean: The Perfect Day attracted 2.13m (9.38%) at 8pm, with Dad's Army pulling in 1.73m (7.91%) at 9pm.
Back on ITV, Paddy McGuinness's dating show Take Me Out entertained 3.24m (14.9%) at 8.40pm,