Glen replaced Ivan Sproule for the final 18 minutes at Pittodrie and the move paid off when the former Hearts man found the net 10 minutes later.
The result leaves County behind Highland neighbours Inverness only on goal difference in what is fast becoming a fairytale season for Derek Adams' side.
The Dons remain outside the top six by a point and will have to await tomorrow's results to see how the table shapes up.
Adams named an unchanged County side following their convincing 3-0 win over Motherwell.
In the wake of the horsemeat scandal, the Pittodrie club had taken meat pies off the menu but made three changes from their draw against Kilmarnock in the hope of beefing up their side.
Out went Gary Naysmith and Rob Milsom, dropped to the bench, and the injured Joe Shaughnessy missed out. In their places came Clark Robertson, Johnny Hayes and Josh Magennis.
Once the sides had settled into the game, the neat play of Ross County saw them begin to boss the midfield but they were struggling to penetrate the Dons defence, and Jamie Langfield's goal remained unthreatened.
Despite that, it was the Dons who were creating the better chances. After 25 minutes, Niall McGinn picked out Ryan Jack at the back post. His shot was disappointing, but the hard-working Hayes kept the play alive and forced Brown to turn the ball behind.
When County did threaten, it was a lack of numbers in attack that was their undoing. Rocco Quinn sent Sproule scampering away down the right a couple of minutes later but with only Sam Morrow to aim at, his low cross was cut out by Russell Anderson.
After 33 minutes, McGinn was forced to come deep to create himself an opportunity but despite Brown's save, diving low to his right, the shot was always fading away from goal.
A couple of minutes later, the visitors earned a corner when Langfield was forced to dive to his left to turn away Sproule's low, right-footed shot.
Sproule had netted four goals in as many games since his move to Dingwall and he looked to be on course for a fifth when Quinn caught Magennis in possession and sent the Northern Irishman clear through the middle, but he used a hand to control the pass and referee Crawford Allan was wise to his trick.
The Dons made a tactical change at the break when they introduced Peter Pawlett in place of the largely ineffective Rory Fallon and reverted to the 4-2-3-1 system they have utilised so often this season.
It was perhaps an acknowledgment of the way County had taken hold of the midfield in the first half, and saw the sides match up man for man in the middle of the park. That Aberdeen's midfield improved markedly thereafter showed the sense in the move.
But it could not counteract the threat of Sproule. Always on the shoulder of the last defender, a 63rd-minute pass from Quinn sent the former Hibs man away again and Langfield did well to block at his near post.
It was perhaps a surprise, then, when Sproule was hauled off to be replaced by Glen after 72 minutes, the former Hearts man joining fellow sub Steffen Wohlfarth in attack.
McGinn, as usual, was the main man in attack for the home side and when Langfield shunned the short pass in favour of route one with 15 minutes to go, the former Celtic man was the target.
He easily turned Scott Boyd but lashed his shot into the side-netting.
Aberdeen had replaced Hughes with Milsom just after the hour, and they threw on teenage striker Declan McManus for Hayes for the final 12 minutes.
But it would be County's changes that paid off. Wohlfarth laid the ball into the path of Glen with nine minutes to go and the 22-year old lifted the ball high past Langfield to open the scoring.
Gavin Rae came close to levelling for the home side when he turned a Pawlett pass towards goal, but Brown got down well to save at his near post.
- Sports & Recreation
- Ivan Sproule
- Jamie Langfield