Robbie Fowler received a hero's welcome on his Anfield return but a late own-goal by Xabi Alonso cancelled out Steven Gerrard's opening goal as ten-man Birmingham clinched a 1-1 draw.
Fowler - introduced as a 63rd minute substitute - would have completed a dream return had not his last minute overhead kick been ruled offside moments after Alonso had embarrassingly levelled for Birmingham.
Nothing but a comfortable home victory was likely to satisfy an expectant Anfield and the crowd saw Liverpool skipper Gerrard send a rising free-kick inches over the Birmingham cross bar after just seven minutes.
Luis Garcia quickly followed his captain's example, drawing a fine save from City keeper Maik Taylor with low drive moments later but that, inexplicably, proved to be Liverpool's last chance for a long while.
Liverpool's normally resolute defence looked decidedly shaky and Benitez's decision to hand Daniel Agger his debut alongside Sami Hyypia looked set to misfire when the Dane gifted City a 20th minute opening.
The former Brondby centre-back presented the ball to former Liverpool striker Emile Heskey and it took a superb save from Jose Reina to deny Chris Sutton's subsequent shot.
But the visitors quickly showed they also possessed the capacity to self-destruct and did so in spectacular style when Damien Johnson tossed away his team-mates' good work with a reckless, high lunge on Agger that earned the Northern Ireland midfielder a red card.
The interval brought relief from a tepid game but Liverpool returned with renewed vigour and quickly carved out headed opportunities for Peter Crouch and Agger.
Then just as Fowler was receiving his final instructions from Benitez before stepping into the action, Fernando Morientes worked his way to the by-line and pulled the ball back for Gerrard whose first time shot deflected off Matthew Upson and beyond Taylor.
But with Liverpool looking sure to claim victory, Pennant's cross was headed down into the six-yard box by Sutton with just two minutes left, only for Alonso to make his howling error which sent the Birmingham fans wild.
There was still time for Hamann to hit the bar and Morientes to see a header deflected over as desperate Liverpool poured forward. Fowler's dramatic overhead kick looked to have provided the returning hero with the perfect start to phase two of his Liverpool career, but it was ruled offside.
