The Baggies boss was able to find some small positives in what he believed was a generally-improved defensive performance at Sheffield United on Tuesday.
But Albion still lost the match, after lapses allowed the Blades to fight back from a goal down to win 2-1 courtesy of second-half goals from Jayden Bogle and Billy Sharp.
The Baggies, who now sit 10 points adrift of safety following Brighton’s shock win at Liverpool on Wednesday night, had gone ahead through Matt Phillips’ 41st-minute goal,
Allardyce said: “The biggest positive from our point of view was not conceding in the first 10 minutes and getting 1-0 up at half-time.
“That’s a small plus for us but we have to start concentrating more.
“Callum Robinson’s chance at 1-1 was the most defining moment in the game.
“Those defining moments are split seconds and that split second of us not going 2-1 up. Ultimately we still shouldn’t have conceded the second goal but we did.
“At 2-1 I don’t think we’d have lost the game. I’m not saying we would have won but those defining moments make a difference.”
Fixing Albion’s defensive frailties is key to Allardyce engineering an escape from relegation which, with 16 games to go, has begun to look a tall order.
Albion, who visit Tottenham on Sunday, have conceded at least twice in all but one of the nine Premier League matches he has taken charge, including their one victory, the 3-2 derby success at Wolves.
They have thrown away winning positions in each of their last two games.
While Allardyce described the majority of their defending at Bramall Lane as ‘excellent’, he was again left to rue the concession of two soft goals.
He said: “We told the players (at half-time) if Sheffield United are going to score it has to be a really good goal. That’s what I’ve said every time we go out: ‘Don’t gift a goal’.
“There were times with the first goal where we could have dealt with it better and got it out of our box, or at least got a block on the shot. Again the same with the second goal.
“It’s very disappointing because we had enough bodies in and around those areas twice to have not let the opposition get a shot off on target.
“Sam Johnstone hasn’t had a difficult save to make. Sheffield United put under pressure, yes, but the vast majority of our defending was excellent.
“But it’s another two goals again, I’ve been saying all along we have to score three to win a game.”
After travelling to Spurs, Albion host Manchester United on Sunday week before a likely defining run of fixtures against Burnley, Brighton and Newcastle, the three teams sat immediately above the relegation zone.