According to overnight data, 30.4% of the audience share watched the remaining contestants go head-to-head as the coaches were joined by guest mentors Katy B, Tinie Tempah, Dante Santiago, Leah McFall and Jake Shears.
In the same timeslot on ITV, 6.4m (27.79%) tuned in to watch the latest episode of Ant & Dec's Saturday Night Takeaway. This week's episode saw the duo go undercover to prank Gordon Ramsay. A further 456,000 (2.01%) watched an hour later on ITV+1.
Back on BBC One, medical drama Casualty entertained 5.15m (25.15%) at 9.20pm, while 4.14m (29.43%) watched the football highlights on Match of the Day at 10.30pm.
BBC Two's biggest ratings of the evening came from classic sitcom Dad's Army, which attracted 1.95m (6.89%) at 7.15pm.
New series The Perfect Morcambe & Wise launched with 1.33m (5.72%) at 7.45pm, followed by Darcey Bussell's Ballerina Heroines which drew in 1.34m (5.94%).
Back to ITV, Philip Schofield's The Cube kicked off its eighth series with 3.75m (16.78%) at 8.20pm, while The Jonathan Ross Show entertained 2.13m (10.69%) with interviews from Dara O'Briain, Kristin Davis, Ice Cube and Claudia Schiffer at 9.20pm.
Channel 4's most-watched programme of the night was weather documentary The Storms That Stole Christmas with 850k (3.7%) at 8pm.
US drama Hostages continued with 620k (2.98%) at 9pm, while a showing of Matthew McConaughey's The Lincoln Lawyer pulled in 790k (5.53%) at 10pm.
Channel 5 brought in 606k (2.72%) with a feature-length episode of NCIS from 6.30pm, followed by Live International Boxing at 9.10pm, which entertained 759k (4.06%).
BBC Four's Salamander once again topped the multichannel ratings. Approximately 852k (4.02%) watched the evening's first episode at 9pm and 797k (4.11%) tuning in to the second instalment at 9.45pm.
ITV3's Inspector Morse prequel Endeavour attracted 773k (3.99%) at 9pm, while Doc Martin was seen by 697k (3.05%) earlier at 8pm.
A showing of Alex Pettyfer's I Am Number Four brought in 638k (3.28%) at 9.10pm on BBC Three.