Harry Maguire bemoaned Manchester United's inability to defend a late set-piece which ultimately cost them two vital points in the 2-2 draw against Southampton.
United had battled back from a goal down to lead at Old Trafford after a quick-fire double from Marcus Rashford and Anthony Martial cancelled out Stuart Armstrong's early strike.
United had been reduced to 10 men following a head injury to substitute Brandon Williams, and were unable to bring on a replacement due to the Premier League's recently introduced substitution rules.
But Southampton piled the pressure late on and got a deserved equaliser deep into stoppage time when Michael Obafemi struck from close range in the 97th minute.
It means United miss the chance to move into third place, and stay in fifth behind Chelsea and Leicester with three games to play as the battle for Champions League qualification ramps up.
And captain Maguire was left to rue his side's failure to defend the set-piece late on, having been a man down and on the verge of securing a crucial victory.
"When you are down to 10 men the one thing you can do is defend set plays, get your head in it and get the ball out of the box but we didn't do that," he told BBC 5Live.
"We can't be doing that if we want to get to where we want to get to.
"The way we try to play and try to build from the back there are times we might get caught on the ball and we have to react quickly. The boys reacted brilliantly.
"We had numerous chances to finish the game off. The second half we had to be better on the ball, [it was] disappointing in the end."
