Sunderland missed the chance to move up to second in League One after they were held to a 1-1 draw by Charlton.
The Black Cats, who were in league action following their FA Cup second-round exit at the hands of Walsall, could have closed the gap on leaders Pompey to four points with victory at Valley Parade.
However, Luke O’Nien’s second-minute opener was cancelled out by a Reece James own goal on 50 minutes, leaving Jack Ross’ side in third place – a point behind second-placed Luton and six adrift of Pompey.
Lee Bowyer’s side move up to fourth following the draw, leapfrogging Barnsley, who lost to Burnley in the FA Cup.
Sunderland, of course, still have another game in hand on both the Blues and Hatters.
Yet dropping two points at a time when their rivals are both in Cup action will represent a blow to the Black Cats’ automatic promotion hopes.
Elsewhere in League One, Conor Chaplin scored his first goal since making his move from Pompey to Coventry permanent.
Yet, it wasn’t enough to stop the Sky Blues going down 2-1 at Scunthorpe.
Meanwhile, Marcus Harness scored in a hat-trick as Burton eased to a 4-0 victory against Rochdale.
Liam Boyce scored the Brewers’ fourth goal.