Series five's eighth episode, 'A Hollow Queen', averaged an impressive 5.81m and achieved a share of 23.8% in the 8pm slot versus X Factor, rising 300k week-on-week.
The BBC fantasy drama's high figures coincide with the announcement that Merlin's current run will be its last.
> Poll: Is it the right time for 'Merlin' to end?
> 'Merlin' exec on new movies: "There's definitely ongoing talk"
> Colin Morgan: 'Merlin has run its natural course'
The X Factor slumped to 8.01m (33.1%) for ABBA and Motown Week on ITV1 (+1: 229,000), coming a distant third to Strictly Come Dancing's colossal 10.25m (42.3%) earlier on.
With ITV dominating after the watershed, I'm a Celebrity... Get Me Out of Here logged 8.03m (36.2%) between 9.45pm and 10.45pm (+1: 497k), after which 639k (4.9%) stuck around for spinoff I'm a Celebrity... Get Me Out of Here Now on ITV2 (+1: 107k).
Earlier in the evening, BBC One won 5.24m (24.9%) for Pointless from 5.45pm, while ITV1 could only muster 2.99m (12.2%) for Take Me Out at 6.45pm (+1: 156k).
Elsewhere, a classic Dad's Army topped BBC Two's night with 2.02m (8.3%) at 8.30pm, 980k (4.3%) watched Channel 4's screening of The Wolfman from 9pm (+1: 176k), and CSI: Miami commanded 1.3m (5.8%) for Channel 5 at 9.45pm (+1: 135k).
Overall, ITV1 topped primetime with 28.1% (+1: 0.8%) versus BBC One's 23.9%. BBC Two was far away in third with 5.4%, beating Channel 5's 3.6% (+1: 0.2%), and Channel 4's 3% (+1: 0.4%).
Danish crime drama The Killing returned to BBC Four with a double bill from 9pm, attracting 834k (3.5%) and 751k (3.5%).
BARB ratings data supplied by Attentional