The Baggies appeared to be cruising towards victory early on in the Barclays Premier League clash at The Hawthorns, with Long having opened the scoring in the third minute and then doubled the hosts' advantage with another goal in the 11th.
They had further chances - Stephane Sessegnon missing a particularly good one - to make it 3-0, but Villa fought back to claim a point.
West Brom failed to react as Karim El Ahmadi converted a 67th-minute volley and nine minutes later, Baggies defender Goran Popov inadvertently headed the ball to Ashley Westwood, who fired it into the net with a fine, swerving drive.
Long told Albion Player: "It's a killer blow, and especially after Chelsea as well, with us all but having the three points there (in their last outing West Brom drew 2-2 at Stamford Bridge, where they conceded a stoppage-time penalty).
"We play good football, but we need to start learning from these mistakes and control the game when we get ahead.
"It was a disappointing night and we have to learn from it going into the Newcastle game (away on Saturday) and make sure we pick up three points."
Long demonstrated superb technique for both his goals.
For his first, he brought down Chris Brunt's long ball expertly with his right foot before lashing in with his left, and for his second, he pounced on a poor attempted pass by Leandro Bacuna and deftly chipped Brad Guzan.
Regarding his opener, the Republic of Ireland international said: "I think nine times out of 10 I wouldn't get a touch like that - I surprised myself!"
Long admits scoring in the Chelsea match - his first goal of the campaign - was important for his confidence.
He now has four goals in his last four games for club and country, and Long said:
"Trying to get that first goal of the season is always a monkey on your back.
"It was a relief. Hopefully I can keep up this form between now and the end of the season and keep my place in the starting XI."
Long, whose Albion contract has until the end of this term left on it plus a one-year option in the club's favour, had looked set to join Hull earlier this season and after that fell through, he spoke about "time running out" and having to consider other options, despite being happy with the Baggies.
West Brom head coach Steve Clarke on Monday expressed his confidence the club "will sit down sometime in the future and sort his (Long's) contract out".
And Long, now on a run of three straight Albion starts, has emphasised he is enjoying himself at the moment.
The 26-year-old said: "When things are going against you, confidence is a big thing for a striker.
"I feel like I'm going into a game looking forward to the 90 minutes rather than looking over my shoulder at the bench.
"I'm enjoying my football at the moment - we're playing some good football at times and hopefully I can keep on the streak I'm on."
Villa boss Paul Lambert had no doubt his side's first-half display was not good enough, but rated their performance in the second - when they were given fresh impetus by the 57th-minute treble substitution that introduced Andreas Weimann, Gabriel Agbonlahor and Fabian Delph to the action - as "excellent".
And asked about his team-talk at the interval, Lambert said: "There were never any teacups flying around or anything like that.
"We said something, but this is not a blame culture - you are in it together.
"Thankfully we got inside their heads. But once they go over that white line, it is on them.
"They have to perform and in the second half I thought they were excellent.
"It was important to get in at half-time at 2-0, and I knew if we scored the next one it would flip the coin."
Both Albion and Villa, 11th and 12th in the table respectively, now have 15 points from 12 games.
Meanwhile, Clarke has confirmed Baggies defender Liam Ridgewell missed the contest due to a calf strain, adding that he has an "outside chance" of featuring against Newcastle.