ITV1's main show slipped slightly to 8.72m (36.6%) from 7.30pm (+1: 249k), but Ryan O'Shaughnessy and Aquabatique's progression to the final was seen by 7.96m (30.2%) at 9.30pm (+1: 274k).
However, the results shows have overall underperformed, with ratings unexpectedly down on last year's semi-final week.
Planet Earth Live kicked off a quiet night on BBC One, with 3.59m (14.6%) in the 8pm hour replacing Watchdog, then a New Tricks repeat had 3.42m (14%).
The Hoarder Next Door continued to shine with its 2.13m (8.7%) at 9pm (+1: 522k) sealing a decent night for Channel 4. Property show Phil Spencer: Secret Agent logged 1.32m (5.5%) an hour earlier at 8pm (+1: 184k).
Grandma's House sunk to 589k (3.2%) for BBC Two at 10pm, while its 9pm predecessor Shakespeare in Italy interested 751k (3.1%).
World's Scariest Weather pulled in 829k (3.4%) to Channel 5 at 8pm, after which 555k (2.3%) watched The Restaurant Inspector.
Overall, ITV1 dominated primetime with 30.8% (+1: 0.9%), far ahead of BBC One's 17.6%. Channel 4 claimed third place with 5.8% (+1: 1.1%), beating BBC Two's 4.8% and Channel 5's 2.6% (+1: 0.2%).
Russell Howard's Good News entertained 745k (3%) at 9pm and 500k (10.4%) just after midnight.
BBC Four's educational lineup of The 2,000-Year-Old Computer (798k/3.3%) and Do We Really Need the Moon (553k/3.2%) also performed well.