The Dubliners will look back on this game as a missed opportunity. Just before half-time, when Portadown were down to 14 men, Wesley refused a kick at the posts and pressed for a try instead.
But a cross-field kick from Dan Van Zyl, who has come out of retirement, was well-defended by Hika Reid's men and winger Richie Thompson was beaten to the ball.
Effectively, there was a six-point swing as during the second half, when Portadown were presented with a similar scenario, they wisely decided to kick for goal through Whitten.
Wesley had the wind and rain at their backs in the opening half and they moved the ball well, with scrum half Van Zyl and centres Brian Hastings and Alan Thompson showing some nice touches.
But Portadown held the edge in the set piece and that offered them a solid platform, from which they sprung Whitten for a try.
Wesley out-half David Smith kicked a penalty midway through the half, leaving the score at 7-3 at the interval.
A great spell of possession rugby, following a dozen rucks, preceeded a try in the corner for full-back Barry McLaughlin.
Nonetheless, two well-struck penalties from Whitten - the second coming five minutes from time - decided this tie and saw Portadown bounce back into the senior ranks with all four points.
At the summit in Division Three, County Carlow are out on their own on five points after their superb seven-try 42-0 hammering of Waterpark.
Australian coach Jason Jones will be keeping Carlow's feet on the ground though.
The midlanders have disappointed in the league in recent years but the signs are good for this term, with qualification for the AIB Cup's second round also in the bag.
A recent weekend training camp had Carlow tuned up for their league opener and they did not disappoint the home crowd.
Richie Whyte, George Campbell and Shannon Brown scored a brace of tries each, while the 18-year-old Matt Dempsey touched down on his AIB League debut.
Rainey Old Boys, meanwhile, claimed their second win away to Banbridge this season.
Having accounted for Bann on a 23-0 score-line in the Ulster Senior League last month, Rhys Botha's men travelled with added confidence.
And although things did not go entirely to plan - Bann's Richard Finlay bagged a converted try and a penalty - the Magherafelt season managed to chalk up a 17-10 win, courtesy of a try from hooker Gary Coleman and Michael Glancy's four-penalty salvo.
Saturday's Leinster derby at Parsonstown finished in a 15-12 victory for Suttonians over hosts Barnhall.
The Dubliners dug deep to nab their third straight league win over the Blue Bulls.
George Flynn, a recent signing from Clontarf, and Vinny Patton scored a try apiece, with Suttonians' former captain Dave Walsh kicking a conversion and the penalty which effectively split the sides.
Third in the division last season, Queen's University got their new campaign off to a positive start with a gutsy 22-16 success at Naas.
The Belfast students were on the end of a heavy beating by Malone in the AIB Cup last week but Brian Robinson and Robbie Moore got a timely response at Forenaughts.
Ian Porter, who featured for Ireland at this year's Under-20 World Championship, was the star man for Queen's. He finished with 12 points (a try, two conversions and a penalty).
Elsewhere, Monastery Field is proving to be a happy hunting ground for Sunday's Well. The Corkmen scored their third successive league win (19-11) at Connemara, with Chris Burnett (a try, conversion and four penalties) scoring all of their points.
New recruit Kenneth Diffenthal landed a penalty and converted a try from back rower Aurelien Casanova as Corinthians beat out Nenagh Ormond (10-3) at Corinthian Park.
And Cork side Midleton also made an impressive start to the league run, cantering out to a 24-3 triumph at home to Ards.
David Lee and James Colbert scored a try apiece for the victors, Jeff Hitchmough kicked 11 points (three penalties and a conversion) and Gary Jones also chipped in with a drop goal.
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