Derby County's League Cup run is over after the Championship club were dumped out at the first hurdle by League Two side Portsmouth.
Paul Clement named a strong side for the first-round clash at Fratton Park in a bid to avoid becoming the latest second-tier casualty following a string of shocks on Tuesday.
However, a team including Darren Bent, Jason Shackell and Andreas Weimann fell behind to Adam McGurk's header early in the second half.
Lee Grant will have been disappointed with his efforts to deny the midfielder but close-season signing Shackell levelled soon after with his first goal since moving back to the club from Burnley.
However, 18-year-old substitute Conor Chaplin had the final say when he fired past Grant 14 minutes from time - ensuring the League Two title favourites a place in the second round.
They will be joined by Middlesbrough - Aitor Karanka's Championship outfit enjoying a much simpler progression than Derby against Oldham Athletic.
After Yanic Wildschut opened the scoring, former Espanyol man and big-name close-season signing Cristhian Stuani weighed in with his first two goals for the club.
Danny Philliskirk's close-range finish made the scoreline more respectable for the hosts but three-time finalists Middlesbrough never looked like bowing out at Boundary Park.
There was no debut for the ineligible Chris Kirkland in Preston North End's 3-1 victory over Crewe Alexandra as Simon Grayson saw Jordan Hugill, Will Keane and Josh Brownhill on target at Gresty Road.
