The Blues have little time to dwell on the defeat ahead of Wednesday's west London derby at Fulham, where victory and a consolidation of a top-four place and Champions League football next term is the main agenda.
"It was a surprise because I thought we were ready physically and mentally," Benitez said of the FA Cup defeat.
"We had to adapt things at half-time. We conceded an early goal (in the second half), but after you could see the reaction of the team.
"That means we were ready, but you have to start from the beginning, not just the second half."