Porter's 76th-minute effort saw him dummy and spin away from a couple of tacklers before stretching over to score by the posts, allowing James McKinney to kick the province to an exciting comeback victory.
Mark Anscombe's pre-match comments that the 'result was not a priority' make have taken some pressure off his players as they ran out for the first time at the revamped Ravenhill, but for the 25-year-old Porter - introduced as a half-time replacement - this was a big chance to impress.
The former Ireland Under-20 international slipped back in Ulster's scrum half pecking order with the arrival of South African star Ruan Pienaar, the strong form of Paul Marshall and recent emergence of fellow Academy graduates Michael Heaney and Blane McIlroy.
Porter made eight senior appearances for Ulster off the bench between September 2010 and April 2012. Ironically, his last outing for the province before Friday's game was against Leinster in Belfast some 16 months ago.
He was back playing for his hometown club Banbridge in the Ulster Bank League last season, at the end of which he received a welcome phone call from the Ulster set-up.
The province were short in the scrum half department following the ending of McIlroy's development deal, so the invitation to take up a short-term contract - similar to Heaney's own one from last season - was gladly accepted by Porter.
"I got the call in late May/June that David (Humphreys) wanted me to come in for six months. It didn't take long for me to think, 'yes, that's what I want to do, I'll give it another shot', and I'm delighted to be back here," he told BBC Sport Northern Ireland after the Leinster game.
"I enjoyed playing with Banbridge last year, my hometown club. But there's nothing quite like running out at Ravenhill on a Friday night...with all the crowd, the stadium, just everything about Ravenhill, it's hard to beat."
Making the step up to provincial level again, Porter admitted: "There were a couple of times I was running about and the referee's whistle went and I thought I'm not that far off being sick here - it was a fairly frenetic pace at times, no matter how much conditioning you do in pre-season it's hard to get into that.
"Ach, I felt sharp enough. We've done a lot of work in pre-season with (strength & conditioning coaches) JD (Jonny Davis) and Kevin (Geary) and I think I'm in pretty good shape."
Porter, who is also a goal-kicking option, agreed that his reintroduction was helped by the number of familiar faces around him in last night's Ulster side including McKinney, his old half-back partner from Queen's.
"That helped big time. There were not a lot of faces there that I didn't know already and the ones I don't know I have gotten to know over the last few weeks. Having James there (at number 10) was another easy link for me.
"Overall we went pretty well as a team. Obviously there's rustiness, it's the first game of the season, it's very wet and slippery out there and there's things to improve on. But I think we're happy enough with how it went."
The addition of Porter to the playing panel is a sign of the depth Humphreys and head coach Anscombe are continuing to build across the northerners' squad.
The New Zealander introduced 12 players for the second half of the interprovincial tie, including new front rowers Bronson Ross and Jonny Murphy, and he was pleased that there were some 'promising signs' from the pre-season opener.
"They (the players) put their hands up, some of them showed that we'll be building a bit of depth in some positions and that's what you want," explained Anscombe.
"A few guys who weren't allowed to play and can't play today will be looking around beside them knowing there's another guy there that wants to challenge for their position.
"It is a fact that it's a long, tough season and you're going to get injuries during the course of the year and you want to have some depth in each position to cover the tough times you're going to have.
"We're getting there, it's not totally right across every position but there's some good depth increasing for the squad as we enter into the new season."