Pompey dropped one place to fifth in the League One standings after a narrow defeat to Burton at Fratton Park.
The 2-1 loss brought to an end a 100 per cent winning start to Danny Cowley's reign as Blues head coach, with Mike Fondop and Joe Powell netting for the visitors either side of the interval.
Charlie Daniels nodded home in the closing stages, but despite the home side dominating possession, they were unable to find an equaliser.