The USA swimmer, who now has 15 golds to his name after winning the freestyle, pulled in 9.7m on BBC One and 470k on temporary digital channel BBC Olympics 1.
For the duration of the coverage between 7pm and 10pm, viewing never dipped below 5m, while BBC Three's screening of the Team GB women's football match against Brazil logged 1.45m (6.2%).
The final of the women's gymnastics attracted a hefty 4.79m (35.3%) to BBC One from 4pm, prior to which Zara Phillips's silver in the equestrian event interested 2.34m (24.9%) from 2pm.
Ben Ainslie's sailing blew 1.13m (8.7%) over to BBC Three between 2pm and 8pm, helping the channel to a new record all-day share of 6.6%.
Olympic Breakfast (1.57m/40.7%) and Olympics Tonight (2.19m/18.6%) continued to flourish in the early morning and late-night hours.
EastEnders and Holby City both held up well on BBC Two, boosting 9pm's Midwives: Delivering Under Pressure which mustered 2.49m (10.2%).
Apart from Emmerdale, Love Your Garden was ITV1's best-rated programme with just 2.07m (8.5%), while Secrets of the Shoplifter grabbed 1.87m (7.6%) for Channel 4 at 9pm (+1: 392k/2.1%).
Despite the heavy competition, CSI continued strongly with 1.51m (6.1%) and 142k (0.7%) on +1, and Big Brother had 1.32m (7%) at 10pm.
Predictably, BBC One topped primetime with 28.4%, while BBC Two soared to second place with 11.9%, while ITV1 struggled with 9.8% (+1: 0.5%) in third. BBC Three followed with 6.5%, comfortably ahead of Channel 4 and Channel 5's 4.1% (C4 +1: 0.8%).
Geordie Shore: Chaos in Cancun was the 12th most-watched multichannel broadcast of the day with 369k (2%) on MTV in its usual 10pm slot.
