Giroud, who captained the gunners in the absence of injured Koscielny scored the winner in the 89th minute and helped maintain Wenger’s record as an FA Cup specialist.
Arsene Wenger have won the FA Cup six times and two times in the last three seasons. He has never been eliminated in the third round.
Wenger gave contract rebels Alexis Sanchez and Mesut Ozil the night off while Santi Cazorla, Koscielny, Francis Coquelin and others were on the treatment table.
Preston North End began very well and gave Arsenal an early scare when they went ahead in 7th minute through Robinson though they could have added to their tally but missed many glorious chances in the first half.
On the restart, just 52 seconds on; Ramsey drew an equalizer when Iwobi laid down the ball for him to fire a low drive shot on the right.
From then, Arsenal began their dominance and showed character and resilience of a premier league team. In the 83rd minute, Oxlade-Chamberlein was substituted for Welbeck to make his long awaited return since injuring his knee ligament eight months ago.
Arsenal played most of the second half in Preston North End half and finally broke their dogged defense when Giroud scored from Lucas Perez back heeled pass to give them a well deserved lead and victory.