Linfield manager David Healy felt his side lacked the necessary "composure" in front of goal during their 1-0 defeat to Glentoran at the Oval on Friday night.
The hosts' captain Marcus Kane had smashed in the opener just before half-time but Declan Devine's side were reduced to 10 men with more than half an hour to play when James Douglas was shown a second yellow card.
The Blues piled on the pressure but could not make the most of their dominance in the second half.
"We didn't show enough composure, enough understanding of what type of finish was needed in the final third," Healy said.
"That's the frustration. There were more than enough opportunities to at least get level.
"The players, I feel as if there's enough quality in the final third of the pitch.
"But when it gets to moments like tonight, it's about that split-second decision - do you go hard? Low? High? Whatever type of finish was needed, we didn't get it right tonight."
Healy said his side "lacked the intensity" and gave up a "really soft goal" in the first half.
After his side's second below-par derby showing of the season - the Glens were 3-1 victors at Windsor Park last month - Healy refused to make any excuses for the result despite a number of penalty claims waved away in the second half.
"Ifs and buts. I don't want to make excuses, I won't," he said of the potential spot-kicks.
"We had enough ball and we had enough time in the final third [to equalise] and we didn't do that."