The North End number two fired home a blistering effort shortly after moving into the midfield to equalise Jed Wallace's third minute opener for the visitors.
Manager Simon Grayson made one enforced change for the clash with Guy Whittingham’s Pompey outfit, Joe Garner a direct replacement for Stuart Beavon, who had a mandatory spell on the sidelines due to being knocked unconscious against Orient the previous week.
Portsmouth took an early lead with what was really their only serious foray into the North End half during the first period and it came as North End were still screaming for a penalty.
The Lilywhites have gone more than a year since their last penalty at Deepdale and Lee Holmes thought he could have earned one after turning Shaun Cooper inside out two and a half minutes into the game, but the referee saw nothing as the winger came down and Pompey broke.
David Connolly picked up a poor ball and was through on goal, Declan Rudd did brilliantly to hold him up and push him wide, but the frontman slid the ball out to Jed Wallace who slotted in from 18 yards out.
North End did everything but score in the opening 45 minutes.
Jack King was the first to find the woodwork in the Lilywhites way, heading Lee Holmes right wing cross against the cross bar on 11 minutes.
A second big shout for a spot kick came two minutes later, this time it was on the opposite flank as Yassin Moutaouakil shoved Will Hayhurst off the ball when the young winger had beaten two men, but again Rob Lewis saw no infringement.
On 17 minutes it was the post that somehow denied North End! Joe Garner hit the inside of left hand upright and a ball ran back along goalline and out for a goal kick after great build up; Mousinho’s deflection falling to the No.14 unmarked, but somehow the ball stayed out.
Two opportunities in quick succession fell to North End centre half Paul Huntington, the rangy No.4 heading Lee Holmes corners, one from each side, both going just past the right hand post.
Three minutes before the break another great opportunity was spurned as Pompey failed to clear and Garner and King left the ball for Holmes who scuffed shot wide of right hand post.
North End were close to drawing level immediately after the break Lee Holmes swinging the ball in from the right and Jack King out-jumping Simon Eastwood and almost heading home.
On 51 minutes Declan Rudd was called into action for the first time since the opening minutes, making a fine save from Pompey skipper Johnny Ertl's long range effort.
It was now all out attack, with Eastwood getting fingertips to Jack King's header to give North End another corner which saw Ertl make a vital block to deny Wroe a chance.
Gyepes, who had been booked in the first half after hauling down Joe Garner, was extremely lucky not to be sent off before the hour mark, Jack King going in the book for making the same foul as the Hungarian within seconds of each other.
On 58 minutes the Pompey keeper made two full stretch saves in 30 seconds to deny King's header and then Mousinho's cross-cum-shot.
As the hour mark passed, manager Simon Grayson made a double change, Paul Connolly and Graham Cummins on for Joe Garner and John Mousinho; Keith Keane going into the midfield; Bailey Wright took the captain's armband.
Cummins tested Eastwood again, meeting Holmes' cross with 20 minutes left, but the former FC Halifax Town stopper was in fine form again.
North End were level with 13 minutes to go and what a goal! Keith Keane with his first for the Club, a stunning control and volley giving Eastwood no chance from the left hand corner of the box.
North End were now rampant and Nicky Wroe exchanged passes with Graham Cummins in the box and almost grabbed North End the lead with a drilled effort from the left byline.
Four minutes of injury time went up on the board, but the game remained level.
PNE line-up: Rudd, Keane, Buchanan, Mousinho (Connolly, 63), Huntington, Wright, Holmes (Monakana, 78), Wroe, Garner (Cummins, 64), King, Hayhurst. Subs not used: Stuckmann, Procter, Beardsley, Foster
Portsmouth line-up: Eastwood, Cooper, Walker (Butler, 57), Connolly (Maloney, 73), Moutaouakil, Gyepes, Ertl, Racon, Agyemang (Akinde, 83), Rocha, Wallace. Subs not used: Smith, Sodje, Harris, Webster.
Referee: Mr R Lewis
Attendance: 9,464 (553 away fans)