Jerome notched his sixth and seventh goals of the season in the first half to lift his side into eighth and leave Pompey further cast adrift at the foot of the Premier League despite Kanu's late consolation.
Pompey may have earned themselves a glamorous FA Cup semi-final against Tottenham or Fulham at Wembley in April, but after their triumph over Blues on Saturday looked to be suffering a hangover.
Jerome's first arrived on 16 minutes as Christian Benitez, one of four players brought into the first eleven in light of the cup defeat, was Birmingham's creator as he slipped a pass clear of the home defence.
Former England Under-21s striker Jerome bounded into space before sending a low drive past David James and in off the far post.
In a half short on incident Pompey's best chance ended up not really being a chance at all.
Jamie O'Hara sent Nadir Belhadj free down the left-hand-side and the Algerian's cross was stood up for Aruna Dindane, but just as the Ivory Coast striker clenched his neck muscle to head goalwards, Barry Ferguson made a vital interception.
Benitez should have made it two moments later as he beat the offside trap but as he dropped his shoulder to round James, Steve Finnan retreated to make a vital last-ditch challenge and rob the Blues striker.
The Ecuadorian atoned for that miss minutes later when, with his back to goal, his delicate back-heel sent Jerome free to double his and his team's tally for the night, placing his finish under James.
Frustrated Pompey boss Avram Grant made a double substitution at half-time introducing the erratic Quincy Owusu-Abeyie and the experience of Greece captain Angelos Basinas to try and breathe some life back into his team.
But it proved another largely lifeless 45 minutes of football with Belhadj's cross just after the hour mark zipping across the face of goal and narrowly missing the outstretched leg of Frederic Piquionne, who dived in vain toward the ball.
Birmingham substitute James McFadden tested James with a low, near-post drive ten minutes from the end, but Kanu set up a nervy final few moments for Alex McLeish's side with a close-range header for his first Premier League goal of the season.