Third-tier Pompey had not beaten Arsenal since a 5-4 league victory in 1958, but they caused the Gunners plenty of problems before the deadlock was broken just before the break. Reiss Nelson's cross was met with a sweetly-timed volley inside the area from Greece international Sokratis who put the Gunners ahead in first-half stoppage time. The goal seemed to give Arsenal an injection of confidence and Nketiah made it 2-0 six minutes after the break, controlling a cross at pace before bundling the ball home from close range. Portsmouth, roared on by their passionate fans, defended well but lacked spark in attack as Arsenal, the FA Cup's most successful side with 13 titles, held on for a comfortable win. 'Tonight I'm so pleased with the team, with everybody, with the young boys. They are improving a lot, every single week, they have a great mentality,' Arsenal defender David Luiz, who wore the captain's armband, told BT Sport. Scorer Nketiah revealed that manager Mikel Arteta had urged his players to increase the tempo and intensity in the second period in order to put the result beyond doubt. 'In the second half we played a lot quicker and obviously that's when the gaps appeared and we were able to play our best football. We came out quite intense in the second half and obviously the early goal helped,' the 20-year-old said. The rest of the fifth-round ties are being played in midweek due to the short winter break in the Premier League, with the draw for the quarter-finals taking place on Wednesday when holders Manchester City visit Sheffield Wednesday.