Leicester City manager Craig Shakespeare was frustrated to concede a set-piece goal to Manchester United forward Marcus Rashford after his side appeared to be closing in on an Old Trafford point.
United won 2-0 in the Premier League on Saturday, with substitutes Rashford and Marouane Fellaini scoring inside the last 20 minutes.
That came after Kasper Schmeichel had produced an inspired performance, saving Romelu Lukaku's second-half penalty as part of a fine individual display, with Leicester defending doggedly to remain in the game until the closing stages.
The manner of Rashford's goal, where he was left in space to convert a Henrikh Mkhitaryan corner from 10 yards, angered Shakespeare.
"I think we frustrated them for large parts of the game," Shakespeare said to BT Sport.
"When you come to Old Trafford in the form they are in, they will have big moments. We had our moments too but could not see the game through.
"Set-pieces are our Achilles heel at the moment. We need to organise and set better.
"It was a harsh penalty but a great save form Kasper Schmeichel. To go 1-0 down, it knocked a bit of spirit from us. Disappointed in the overall result, but we were nice and solid for large parts."
Leicester defender Harry Maguire had a similar viewpoint after battling to play through the full 90 minutes despite Shakespeare revealing he had been carrying a knock.
Maguire said: "They have waves of attacks and you expect that here at Old Trafford. We came all that way, 60 minutes at 0-0, then at 70 minutes and then we concede from a set play.
"To come to Old Trafford and allow a set-piece to go in is disappointing. To let Rashford have that much time and space is very disappointing for us."
Leicester, who also lost away to Arsenal in a tough start to their season, have three points from as many matches, while United are top of the table with a maximum nine.