A late replacement for Keith Watson, Erskine grabbed the winner for under-par United with just three minutes to go. He was aided by a goalkeeping error from County's Antonio Reguero, who punched a Gary Mackay-Steven corner straight to the sub.
"We had a few opportunities," said United manager Jackie McNamara, "And we got in behind them a few times, but the last pass or decision-making wasn't good, so I put Chris on to give us a bit of composure. I'm delighted he scored the winner. He scored at Pittodrie and his attitude has been first class. He's possibly a bit down because he hasn't started a match yet although there is no reason for him, in terms of what he has done, not to merit a start."
There were early indications in United's play of a certain measure of caution, a hangover, perhaps, from last week's 6-1 drubbing at Celtic Park. Or had McNamara called for his side to show patience in their attempts to find a way past County's stoic defence?
They only found their feet and grew into their passing game after Nadir Ciftci's opener on 19 minutes eased the pressure. The Turkish striker's header at the back post was set up by Paul Paton's well-placed free-kick from the left.
This was a cue for United to turn on the style without causing to many additional worries for County, although Richard Brittain did well to block Mario Bilate's strike in the area shortly before the break.
His intervention garnered even more importance seven minutes after the restart when, as United bombarded the Highlanders' goal only to be thwarted several times by fine defending, the ball broke to Joe Cardle. With McNamara's defence exposed, he sent Graham Carey into space on the left and his expertly judged cross found Jake Jervis, whose side-footed volley brought County level.
A similar manoeuvre almost inflicted further damage on the Tangerines less than ten minutes later. This time it was Uros Celcer who provided the cross, only for Yohan Arquin's header to miss the target by a short distance.
That provoked the home team, who began to sizzle. The final ball, however, invariably lacked the necessary finish, although a Connor Townsend cross and Ciftci header allowed Reguero to effect the most acrobatic of one-handed stops.
There was another "How did he miss that?" query 12 minutes from time when Carey, enjoying an enormous amount of space on the left, found Jervis once more, only for the striker's volley from 12 yards to miss the target.
Erskine's winning strike was a sickener for the Staggies, with manager Derek Adams insisting last night that the home side had "stolen the win".
"Our keeper Reguero is upset with his mistake," the County boss added. "To lose a goal so late in the game after the chances we had was disappointing. They've stolen the three points today, I don't think anyone could have any doubts about that."