The show, which sees Kelly Clarkson, John Legend, Robin Thicke and Jennifer Nettles performing duets with aspiring stars, grabbed 6.7m (1.7) between 8pm and 10pm.
Despite airing in the summer, the figures are significantly lower than recent reality show launches on other major networks, such as Fox's The X Factor and The Voice.
So You Think You Can Dance opened its ninth run with a lower audience than Duets with 6.2m, but a stronger performance in the metered markets, drawing a 2.4 rating with 18-49 adults.
Canadian police drama Rookie Blue returned for its third season with 6m (1.4), slightly off last year's equivalent episode but fairly in line with the Alphabet Network's summer 10pm slot average.
Meanwhile, Jason Isaacs's Awake benefited slightly from CBS's move to repeats, rising to 2.9m (0.9) for NBC.
Perez Hilton All Access was The CW's only new broadcast of the night, securing 870k (0.3) for the network in the 8pm hour.