Barnsley’s seven match unbeaten run came to an end as Portsmouth scored two goals in two minutes.
Managerless Portsmouth put the departure of Steve Cotterill behind them as the second-half goals ended Barnsley’s unbeaten away record.
Stuart Gray and Guy Whittingham were placed in temporary charge this week and masterminded Portsmouth’s third win of the season.
Barnsley had been the better side for much of the first half and struck the post through Jacob Butterfield.
But the home side were well on top when David Norris struck in the 61st minute and they quickly added a second through Luke Varney as Barnsley’s seven-game unbeaten run came to an abrupt halt.
Barnsley created the first real opening in the eighth minute when Butterfield made space to fire in a well-struck shot which Portsmouth goalkeeper Stephen Henderson was able to push away.
Barnsley remained the more dangerous side and Ricardo Vaz Te wasted two great opportunities in quick succession midway through the first half.
See Monday’s Star for the full match report and reaction.