Benjamin had given Cambridge their chance of glory with his first-leg effort at Hillsborough last week - and he was on target again to take his team though to the third round.
The visitors had some early chances. Wednesday's Italian pair, Paolo Di Canio and Benito Carbone, who had been heavily criticised by their manager, Danny Wilson, after the first leg, combined to create an opportunity for Lee Briscoe, who headed over from close range.
The Dutchman Wim Jonk had a shot deflected behind for a corner but from then on it was the home side who looked the top-flight outfit, as Cambridge repeatedly hurried Wednesday into errors. Jon Newsome was booked for bringing down Benjamin after 15 minutes and Peter Atherton followed him for a foul on the teenage striker on the half hour.
Wednesday came more into the game as the half progressed, with Di Canio blasting his 28th minute effort straight at Arjan van Heusden. Carbone had got little change from Cambridge's left-back Jamie Campbell and, after an innocuous tussle, fell to the floor clutching his face.
Booed by the fans, the next meeting of the pair saw the Italian clutching his ankle. He left the field and, despite treatment, was replaced by Niclas Alexandersson a minute before the break.
After two minutes of the second period Jonk's effort was acrobatically palmed away to safety by Van Heusden. At the other end Benjamin almost found a way through after 55 minutes following some confusion in the Owls' defence, but his shot on the turn was cleared off the line by Jonk.
Wednesday made the breakthrough after 68 minutes in somewhat comical fashion. A long goal-kick by Pressman reached Campbell, and the defender's back header beat his own keeper to bring the tie level on aggregate.
However Cambridge, and Benjamin, were not to be denied. Six minutes later the big striker met Alex Russell's free-kick with his head and his effort looped over a helpless Pressman into the top corner.
Taylor could have saved the home side a tense final eight minutes, but his shot came back off the bar and away to safety.
Cambridge United (4-4-2): Van Heusden; Chenery, Duncan, Joseph, Campbell; Mustoe, Wanless, Taylor, Russell; Butler, Benjamin. Substitutes not used: Preece, Marshall (gk), Youngs, Wilde, McCammon.
Sheffield Wednesday (4-4-2): Pressman; Thome, Newsome (Barrett, 76), Walker, Hinchcliffe; Atherton, Briscoe, Jonk (Sanetti, 76), Carbone (Alexandersson, 44); Di Canio, Booth. Substitutes not used: Clarke (gk), Magilton.
Referee: M Halsey (Welwyn Garden City).Reuse content