Morecambe responded well and soon equalised when Mark Hughes's looping header bounced in off the underside of the bar.
However, they missed the chance to go in front when Amond's penalty was saved by Portsmouth keeper Trevor Carson.
Jervis then heaped more misery on Morecambe before the break when he tapped home Marcos Painter's ball into the box for his second of the game.
Redshaw equalised for the hosts 15 minutes from time when his effort squirmed under Carson.
Robbie Threlfall curled over the bar as Morecambe looked for a winner but Portsmouth held firm to take home a point.