Everton manager Roberto Martinez felt his side let an opportunity slip after they were beaten 1-0 by Manchester United on Sunday.
In a game of few chances at Old Trafford, Anthony Martial's 54th-minute goal was the difference between the sides.
Phil Jagielka went closest for the visitors when he headed against the bar, but they could not grab an equaliser and avoid a third straight Premier League defeat.
"It is a real disappointment," Martinez told Sky Sports. "You get that nearly feeling. We stopped Manchester United from controlling the game and we are very disappointed with the goal, but from then we had the better chances.
"All in all we need to do much better in terms of being able to get a better result out of the performance. The difference between the two teams was minimal and we lost the game, and that's the disappointing thing.
"The game was in our hands to affect the result and you probably don't expect that Old Trafford. Maybe you hope for a result and hope the home team allows you to get something, but I felt the performance was so level between the two sides - it is really disappointing."
The loss leaves Everton in the bottom half of the table and continues their inconsistent form this season.
But they do still have an FA Cup semi-final against either West Ham or Man Utd to look forward to, and Martinez hopes they can finish the campaign on a high.
"We need to regroup," he said. "We are still getting through an important period. We had an important win in between the last two defeats (against Chelsea in the FA Cup).
"One defeat was in 12 minutes when we were down to 10 men, that performance deserved a lot more. Out of the last three games only the performance against Arsenal was terrible and at a level we did not expect.
"Today was different, we could have executed better in certain moments and we conceded a very soft goal. From now until the end of the season we need to display a better mentality."