Olivier Giroud and Aaron Ramsey conceded Arsenal were taken aback by Preston North End's desire and intensity in the first half of their FA Cup third-round meeting at Deepdale on Saturday.
The Gunners started woefully and found themselves 1-0 down inside seven minutes thanks to Callum Robinson, who could have had a second midway through the half.
Jordan Hugill and Paul Gallagher also missed excellent chances for North End in the opening 45 minutes before Arsenal improved markedly after the interval.
Ramsey levelled matters within 60 seconds of the restart and Giroud netted the winner a minute from time for his 10th goal in his last eight starts for the club.