Mark Hughes felt VAR should have been used to award Southampton a goal and a penalty during their FA Cup semi-final loss to Chelsea on Sunday.
Second-half goals from Olivier Giroud and Alvaro Morata sent Antonio Conte's men into the final for the second year in a row, with Manchester United awaiting.
"We're disappointed obviously, in the first half we didn't affect them as much as we talked about but we were pleased to go in at 0-0 at half-time as they had chances," Hughes told BT Sport.
"[After] coming out and going behind early [in the second half], the response was good. We are disappointed with the nature of the goal and we should've done better and cleared it.
"We needed a response and got that. We had no luck, the keeper made a glaring mistake and miscontrolled it. I assumed VAR was in operation and it was a clear opportunity or situation to review and get it correct.
"Clearly, they didn't. I don't know how they make a key decision that quick, I don't know if the referee gets information in his ear, but Charlie has done nothing wrong and it should have reviewed. There was also a clear handball by Giroud from the following corner, so we feel hard done by."
Great effort today from everyone involved with fans were superb we just come up short today, was it a foul I’m not sure... var April 22, 2018
Southampton have four fixtures left to save their Premier League status with a four-point gap to make up on Swansea City, who they face in the penultimate match of the campaign.
"The second half was more like we needed to be," Hughes added. "Huge game next weekend [at home to Bournemouth].
"[We have] disappointment now because we wanted to progress, but we have to put it behind us and move on for next week."
2 - Mark Hughes is just the second manager to be eliminated from the FA Cup as manager of two Premier League teams (Stoke and Southampton) in a single season, after Glenn Hoddle in 2000-01 with Southampton and Spurs. Magic? April 22, 2018
