The Brewers dominated for large periods at Anstey Park, but ultimately paid the price for missed chances and defensive mistakes.
The visitors took the lead in the 33rd minute when Christopher Machay intercepted a poor back pass. Machay’s effort was saved by Alton goalkeeper Lewis Mees, but York tapped in the rebound.
The home side regrouped strongly at the interval and dominated the second half.
Substitute Erickson Mukambi made a good impact off the bench, and Alton’s equaliser arrived on 60 minutes when Richie Hunter scored from close range.
The home side pushed hard for a winner, and created numerous chances.
Sheerwater appeared happy with a point, until the Brewers suffered a sucker punch in the 91st minute when a long punt up the pitch by visiting goalkeeper Chris Adams found Andre Smith, who coolly finished past Mees.
And Adair was left to rue his side failing to make the most of their dominance in the game.
“I think you’ve got to look at the missed chances and the defensive mistakes,” he said.
“For the first 25 minutes I thought we started the game as well as we have done all season. We got an early goal, and were positive and were on the front foot.
“You’ve got to give Sheerwater a bit of credit for their first goal, which was well worked, but we’ve not picked up the turnover of the ball and the transition from attack into defence was not good enough.
“The second goal is a mistake, which happens. Our keeper hasn’t had much to do, bar the three goals, but that probably speaks volumes for Sheerwater in front of goal.
“We’ve had numerous chances – but their keeper has probably only had to make three saves.
“I don’t know if I’ve seen a more one-sided half than the second half, but you’ve got to give them credit as they’ve defended resolutely.
“We got the equalising goal, and then it was just a case of could we get another one?
“But then their goalkeeper has kicked the ball 80 yards down the pitch, we don’t meet the first ball, we don’t cover in behind and they score.
“To be honest, for the levels we should be at it, we probably didn’t deserve anything.
“You can dominate periods of games, but what makes the difference is you scoring and you stopping them scoring.”
While Adair was pleased with large parts of his team’s display, he stressed the need for his side to start picking up results again soon.
“We’re in a results industry here, and nobody talks about how good you were in 83 minutes of a game when you’ve gone away and you’ve got zero points from it,” said Adair.
“We haven’t been getting much luck lately, but when you’re on a tough run you don’t often get luck. You’ve got to make your own luck.”