Mario Soares’ memorable long-range strike to mark his first senior competitive goal proved the highlight as Portadown progressed past spirited Larne.
An injury-time goal by Guillaume Keke forced extra-time on Tuesday night to reward Larne for a determined display.
However, the Ports had a Michael Gault goal and superb Soares finish to thank for extra-time control before Darren Murray closed the scoring with his second of the evening.
Murray kicked off the second-round tie by breaking the deadlock with a close-range finish on 54 minutes after Chris Casement’s free-kick caused problems for Paddy Flood.
Portadown had a goal ruled out before the half-hour mark, with Paul Maguire firing just past the target for the hosts.
Keke pushed the tie into extra-time but Portadown grabbed control courtesy of captain Gault’s header off a Ross Redman corner-kick.
Substitute Soares enjoyed an immediate impact and Murray’s individual effort wrapped up the evening.
Portadown had Billy Brennan to thank for a fine save in extra-time off Keke’s header.
“Those cup ties are always difficult so it comes down to the result as the important factor,” said Ports boss Ronnie McFall. “It was not a great match, with the grass long and the pitch difficult.
“But we displayed the right character overall to get the win and progress into the next round of the competition.
“Although nothing is happening in terms of transfer interest from clubs in Scotland, Darren is certainly looking really sharp at the minute.
“It was a great moment for Marcio Soares to score his first senior goal and one positive from our situation is how it opens up the door for young players.
“It is up to those handed the chance to make the most of any opportunity.”
PORTADOWN: Billy Brennan, Chris Casement, Ross Redman, Garry Breen, Sean Mackle, Michael Gault, Darren Murray, Gary Twigg, Robert Garrett, Jake Richardson. Subs: Chris Ramsey (on for Breen, 21 mins), Marcio Soares (on for Twigg, 118 mins), Christian Stewart (on for Richardson, 103 mins), Jordan Lyttle, Matthew Parker.