Portsmouth won the first meeting, 7-4, in late September.
Reading's 44 goals-against are second worst in the league to last-place Derby's 46. Reading is in 13th place, five points above the relegation zone.
However, Hahnemann's contract with Reading has been extended through the 2008-09 season thanks to a clause that triggered an automatic one-year extension after he played his 20th EPL game of this season.
The 35-year-old Hahnemann has been Reading's No. 1 goalkeeper for six seasons.