Aarons scored two goals - one of which was a sensational overhead kick - and set up another to show Steve McClaren of his qualities.
With Fabricio Coloccini, Mike Williamson, Steven Taylor and Jamaal Lascelles all left out of the side because of concerns about their ability to perform on an artificial pitch, a patched-up Newcastle defence conceded a succession of soft goals as Portland claimed a 4-1 advantage.
Aarons' late double provided a degree of respectability, but questions are being asked as to why the Magpies chose to play a game on a surface that meant McClaren had to field a back four featuing Aarons, Shane Ferguson, Lubo Satka and Gael Bigirimana.
Having claimed a seventh-minute lead through summer signing Georginio Wijnaldum's first goal in a Newcastle shirt, the Magpies were pegged back when Satka inexplicably conceded possession on the edge of his own area, enabling Fatawa Safiu to score.
Anthony Manning headed Portland into the lead midway through the first half, with Taylor Peay adding another goal minutes later as the Newcastle defence made a complete hash of trying to defend a corner.
Bigirimana was at fault as Nick Besler headed home a fourth Portland goal in the second half, before Aarons scored the goal of the game as he teed himself up for a ten-yard bicycle kick that scorched into the net.
Aarons scored again with a long-range effort that found the net via the underside of the crossbar, but United were unable to claim the equaliser that would have enabled them to avoid leaving America on the back of their second pre-season defeat.
Newcastle will return to action at Sheffield United on Sunday, with new signing Aleksandar Mitrovic expected to make his first appearance for the club at Bramall Lane.
Newcastle: Darlow (Woodman 46), Bigirimana, Satka, Ferguson, Aarons; Abeid (Anita 65), Wijnaldum (Janmaat 46), Gouffran (De Jong 76), Sissoko (Obertan 46), Ayoze, Cisse (Armstrong 46).
THE TOON'S GREATEST 100 PLAYERS ... EVER!
This book is a collection of the 100 Greatest Newcastle United players of all time, as voted for by NewcastleUtd-Mad.co.uk readers and a panel of journalists who contribute to the website. The players are in an order of five-per-chapter, counting down from 100 to Newcastle United's greatest ever player (as viewed by the author), but the whole point of the book is for YOU (the reader) to decide who goes where. The list is not, by any means, definitive. As with all books of this nature, whether it be "Greatest Albums"; "Best Movies Of All Time"; or "Top 100 Pin-Ups Of The Year" ... no two people have exactly the same opinion. There will be controversy over who is on the list, and chances are, more controversy over who is not. Here are the best of the best. I have painted the picture with each player's profile. Where they end up in the league of NUFC's Greatest is up to you. Because YOU have the final word.
Otherwise ... if you want a signed copy (for a birthday, etc) for £9.95 and no postage ... you can meet me before a match and I will bring a copy along.
Get in touch: Kevnumad@fsmail.net
NEWCASTLE UNITED
Fri 10th July (8pm BST)
Gateshead FC 0 Newcastle Utd 1 (Cisse pen)
(First half): Darlow, Janmaat, Haidara, Lascelles, Williamson, Anita, Colback, Gouffran, Cisse, Sissoko, De Jong. (Second half): Woodman, Bigirimana, Satka, Good, Ferguson, Tiote, Obertan, Aarons, Perez, Armstrong, Riviere.
Tue 14th July (8pm CT)
Club Atlas (MEX) 2 Newcastle Utd 1 (Sissoko)
Krul (Darlow 46); Janmaat (Bigirimana 72), Williamson, Lascelles, Haidara (Ferguson 72); Anita, Colback; Sissoko (Obertan 72), de Jong (Perez 72), Gouffran (Aarons 72); Cisse (Armstrong 72).
Sat 18th July (8pm UTC)
Sacramento Republic FC (USA) 0 Newcastle Utd 1 (og)
Krul (Woodman 46), Janmaat, Williamson, Lascelles (Taylor 46), Haïdara, Anita, Colback, Sissoko, Obertan (Aarons 69), de Jong (Perez 69), Cissé (Wijnaldum 69).
Tue 21st July (7.30pm UTC)
Portland Timbers (USA) 4 Newcastle Utd 3 (Wijnaldum, Aarons 2)
Darlow (Woodman 46), Bigirimana, Satka, Ferguson, Aarons; Abeid (Anita 65), Wijnaldum (Janmaat 46), Gouffran (De Jong 76), Sissoko (Obertan 46), Ayoze, Cisse (Armstrong 46).
Sun 26th July (1pm BST)
Sheffield United at Bramall Lane
Wed 29th July (7.45pm BST)
York City at Bootham Crescent
Sat 1st August (3pm BST)
Borussia Mönchengladbach (GER) at St. James’ Park
PREMIER LEAGUE
Sunday August 9
13:30 Newcastle United v Southampton
Saturday August 15
15:00 Swansea City v Newcastle United
Saturday August 22
12:45 Man Utd v Newcastle United
Saturday August 29
12:45 Newcastle United v Arsenal
Monday September 14
20:00 West Ham United v Newcastle United
Saturday September 19
15:00 Newcastle United v Watford
Saturday September 26
17:30 Newcastle United v Chelsea