The Light Blues bowed out of the competition in Greenock as Cole McKinnon’s thunderous strike with the game poised at 3-2 was adjudged not to have crossed the goalline after thundering off the underside of the crossbar.
Rhys McCabe’s free-kick then put the game to bed in injury time as David McCallum’s side reflected on a missed opportunity.
Speaking to RangersTV, captain Fraser commented: “It was a really good level of opposition and a side in the Championship. We had chances, but we weren’t clinical. They’re a high level opposition and they’ve effectively killed the game with four great goals.
“It was great play leading into the shot and I felt it was a goal on the pitch, but the linesman doesn’t give it and they go kill the game a few minutes later. It’s fine margins and a disappointing one to take, but we’ll move on.
“I feel that it was an opportunity missed. We came in with a lot of confidence and we really wanted to progress. I felt at stages of the game we done really well, but overall we didn’t get a complete performance.”
Gers B took an early lead in the contest as 16-year-old Josh Gentles stroked home, but the Diamonds flexed their Scottish Championship muscles to turn the game on its head.
And Fraser believes the Lanarkshire side showed the importance of being clinical when opportunities arise in these matches.
He added: “The defending wasn’t good enough at times and they punished us. We’ll certainly do our work back on the training pitch and try to improve moving forward.
“It was really good to still be in the competition and we had some really good games where we’ve done really well. The end goal was to collect the trophy and give ourselves an opportunity to get to a final, but we haven’t done. It’s about moving forward now.”