Portstewart’s hopes of causing a cup upset were dashed by Portadown.
Second half strikes by Gary Twigg and Darren Murray secured the Premiership side’s passage into the quarter finals, but they were made to work all the way by Gary Taylor’s battlers.
The visitors made heavy weather of the first half at the seaside as the hosts proved they were going to be no pushovers in frontof a large crowd at Seahaven.
Portadown were fortunate to see the offside flag raised against Ryan Doherty as he bore down on goal with only six minutes gone.
Chances were proving hard to come by for Ronnie McFall’s men. Murray and Gary Breen failed to hit the target when opportunities did fall to them during the first half.
Ross Redman did force a save right on half time, but it never troubled Joel Maddison in the home goal, who smothered the ball easily.
The Shamrock Park outfit were more assertive after the break with Murray trying his luck from distance just seconds after the restart, it was always going wide of the target though.
Maddison was at his best to deny the striker on 66 minutes as Murray swivelled before thundering a volley goalwards, the keeper though showed great reactions to palm it over the bar.
The deadlock was finally broken with 13 minutes to go. Mackle’s cross found Twigg unmarked at the back post, his initial effort was saved by Maddison, but the ball hit the post and bounced kindly for Twigg to slot home.
Portadown wrapped up the tie with three minutes to go as Maddison could only parry Tim Mouncey’s long range effort, and Murray reacted the quickest to fire in the rebound from close range.
Portstewart: Maddison, Bradley, Campbell, Neill, Peden, Forgrave, Vauls, Millar (Murray 90), Doherty, Turner (McClements 83), Stewart (Donnell 74).
Portadown: Miskelly, Richardson, Redman, O’Hara, Breen, Conaty (Mackle 65), Garrett, Mouncey, McMahon, Twigg (Soares 83), Murray.