Nicky Ajose's first Charlton goal of the season gave the Addicks a precious 1-0 victory over League One play-off rivals Portsmouth at Fratton Park.Ajose bagged the winner five minutes before half-time, slotting calmly past goalkeeper Luke McGee after strike partner Josh Magennis had nodded the ball into his path.Both teams started nervously but Charlton were unlucky not to take the lead in the 21st minute.Jake Forster-Caskey saw his long-range shot deflected wide and from the resulting corner Forster-Caskey's goal-bound effort was cleared off the line by Nathan Thompson.Pompey were poor throughout the first half and Matt Clarke's tame header from a Gareth Evans free-kick was their only shot on target.Charlton came close to a second goal when Ben Reeves shaved the post with a volley from the edge of the penalty area after Forster-Caskey's corner had been only half cleared.Visiting goalkeeper Ben Amos saved smartly from Pompey substitute Connor Ronan and captain Brett Pitman as the hosts pushed for a late equaliser.