Nicky Maynard's brace gave relegation-threatened Bristol City all three points this afternoon at the New Den.
Jay Simpson scored for the home side between Maynard's efforts but it was the visitors who claimed the win against in-form Millwall.
The Lions had an early penalty shout turned down before Maynard opened the scoring with a cool finish from Neil Kilkenny's through pass.
Millwall's equaliser came 12 minutes after the break when Simpson fired home from close range following good work from Henderson and Liam Trotter.
Maynard ensured the scores weren't level for long, restoring the Robins' lead five minutes later by smashing past David Forde after nifty work from strike partner Albert Adomah.
Derek McInnes's side remain in the bottom three but have edged four points clear of the bottom pair of Coventry and Doncaster, while Millwall remain 20th.
