The superhero drama was the most-watched CW premiere for three years, and won the network its best 18-49 demo rating in two years.
It scored a rating of 1.3, with an audience figure of 4.01 million at 8pm.
Supernatural benefited from the premiere, by rising from last week to 1.0 (2.58m) at 9pm.
Fox won the 18-49 demo rating overall, despite The X Factor USA dropping slightly from last week to 3.4 (9.35m) at 8pm.
CBS won the night in terms of total viewers, with Survivor: Philippines falling four tenths to 2.6 (9.57m) at 8pm.
Criminal Minds also dropped a tenth to 3.0 (11.35m) at 9pm. CSI rose a tenth from its last original episode to 2.6 (10.58m) at 10pm.
ABC's The Middle climbed two tenths to 2.4 (7.80m) at 8pm, while The Neighbors evened out with 1.9 (6.27m) at 8.30pm.
A Modern Family double-bill scored 4.7 and 4.9 ratings at 9pm and 9.30pm, down from its 5.5 premiere rating two weeks ago. However, it was the most watched show of the night, taking in 12.03m and 12.22m viewers.
The premiere of Nashville achieved a 2.8 rating (8.97m) at 10pm.
NBC's Animal Practice fell two tenths to 1.1 (3.87m) at 8pm. Guys With Kids also fell by the same amount to 1.4 (4.19m) at 8.30pm.
Law & Order: SVU fell to 1.8 (6.18m), its lowest ever fall score. Chicago Fire premiered with a 1.9 rating (6.43m) at 10pm.