Watford substitute Will Hoskins put goalkeeper Heinz Muller under pressure and did well to square the ball back across the six-yard box and Tommy Smith was in the right place to bundle in his 16th of the season to earn the Hornets a 1-1 draw.
"Those were going to be my exact words; how cruel it is," said the Tykes boss.
"At least we have a point, but it should have been three. It was snatched from the jaws of victory and we've conceded late on, which was disappointing.
"That would have been a nice three points towards what we need to do, but we've got to stay positive, focus on what's in hand and make sure now we're ready for Monday.
"It was always going to be a difficult game, but we started with three strikers to see if we could get a little bit more firepower up there.
"We changed it around a little bit and ended up going 4-4-2. We put Adam [Hammill] on, he had an impact straight away, we got the goal and we looked comfortable and didn't look like we was going to be in any trouble.
"But then a free-kick was planted in our box and it ends up in the back of our net."
Watford are still not mathematically safe, but such has been the scale of their improvement under Brendan Rodgers this was the second consecutive home game they had expected to win but did not, following the midweek draw with Southampton.
Even so, the Watford boss was still pleased with the outcome.
"It was a good point for us," said Rodgers.
"Barnsley are a good side. We were fighting against history and everything today because I think Watford haven't beaten Barnsley since 2001, and obviously when we went behind we weren't at our best. But great resolve and commitment was once again shown in the team.
"I went to two games yesterday and saw not very good performances but we're at that point of the season where the results are very, very important.
"So for us, in every aspect today, psychologically the point was massive, and in terms of where we're trying to go, into that top 12, we moved up another place."
Watford were not at their best, but they were unlucky not to take the lead in the 22nd minute with a move down the middle of the pitch.
It that started with a clearance from keeper Scott Loach, went through Jack Cork and Jobi McAnuff and ended with Ross Jenkins feeding Tamas Priskin, who struck an early right-footed shot from the edge of the area that beat the dive of Muller but not his right-hand post.
Barnsley also struck the woodwork moments later though, albeit in somewhat more fortuitous fashion, with Bobby Hassell's cross from the right appearing to deceive Loach as it cleared him and rebounded down off his crossbar.
However, the visitors did find the net after 67 minutes when Hammill twisted and turned on the right before swinging a cross into the heart of the six-yard box where Macken was the first player to react to convert right-footed from close range.
It looked like it was going to be enough, until Hoskins and Smith had other ideas late on.