Ten-man Pompey looked to be heading for victory after fighting back from 1-0 down thanks to Matthew Taylor's superb double.
Angel earned Villa a share of the spoils with his seventh goal of the season, eight minutes from time and two minutes after Matthew Taylor had given the home side the lead with the second penalty of this topsy-turvy match.
It took until the 11th minute for Portsmouth to launch the first meaningful attack with Matthew Taylor and Gary O'Neil combining well down the right before Gareth Barry came sliding in to knock the ball away for a corner.
Stuart Taylor was called into action for the first time in the 19th minute when he pushed Matthew Taylor's driven 25-yard free kick around a post.
Pompey were forced into an early substitution when Lomana LuaLua was left reeling in agony after turning his ankle and hobbled off to be replaced by Benjani in the 33rd minute.
Harry Redknapp's misery was compounded when Barry put Villa ahead from the spot three minutes later.
Glen Johnson lost the ball in midfield before Steve Davis played in Gabriel Agbonlahor and David James came racing out of his goal to scythe down the England Under-21 striker.
James was lucky to escape a red card but visiting captain Barry gave his former Villa Park team-mate no further let off, slamming his kick into the top right-hand corner.
Matthew Taylor drew Pompey level within seven minutes of the re-start, heading in substitute Benjani's pinpoint right-wing cross at the back post.
Benjani showed why he has found goals hard to come by since his club record £4.1million move from Auxerre in January with a wild volley over the crossbar in the 59th minute.
James made amends for his penalty give away with two superb saves in the space of a minute soon after.
First James dived to his left to keep out Milan Baros' downward header from Liam Ridgewell's cross.
The veteran former England star lived up to his Superman haircut when he came flying across his goal to tip Barry's quickly taken free-kick over the bar after Pedro Mendes had brought down Agbonlahor 20 yards out.
Benjani fluffed another golden chance 20 minutes from time after O'Neil had cut in from the right before laying off the perfect pass and the hapless Zimbabwean blazed over from ten yards.
Barry gifted Pompey the chance to take the lead ten minutes from time when he crazily handled Matthew Taylor's header from O'Neil's in-swinging free kick.
Referee Uriah Rennie again had no hesitation in pointing to the spot and Matthew Taylor coolly stepped up to hammer the ball into the bottom left-hand corner.
Villa were back on terms inside of two minutes when substitute Angel beat James with a rasping right-foot shot from the edge of the area after a poor clearance from Sol Campbell.