Mark Hughes criticised referee Craig Pawson for awarding the stoppage-time penalty that allowed Sunderland to claim a 1-1 draw at Stoke City.
Marko Arnautovic gave the hosts a 50th-minute lead as they responded impressively to three heavy defeats heading into the match.
Relegation-threatened Sunderland pushed for an equaliser during the closing stages, with their pressure rewarded when Geoff Cameron brought down Jermain Defoe and the experienced striker dispatched his 14th Premier League goal of the season from the spot.
Hughes told his post-match media conference: "I thought it was a soft penalty. At that stage of the game we'd seen almost everything off quite comfortably.
"We're disappointed because performance-wise it was significantly better than what we've produced in recent weeks.
"But we're disappointed because we all felt the referee played a part in allowing them to get something out of the game which, in comparison to what we produced, they didn't deserve."
Hughes made five changes from last week's 4-0 loss to Manchester City, and he praised recalled duo Charlie Adam and Peter Crouch - the towering striker setting up Arnautovic's goal on just his third league start of the campaign.
"The guys that came in acquitted themselves really well. Peter Crouch did excellent up top," the Welshman added.
"Charlie Adam came into midfield and I thought he was good up until the point he started to tire.
"In terms of the performance I thought we did okay but felt the only way Sunderland were going to take something out of the game was if a decision went against us. Unfortunately, it did."
Arnautovic went off shortly after his goal having defied an injury-plagued week to start.
Hughes continued: "Marko didn't train all week. He put his hand up this morning and said he wanted to play.
"He took his goal well, got us into a winning position but he couldn't continue
"He has an issue with the muscle at the top of his thigh. When he gets tired it starts to cramp up on him. We hope he's going to be alright for next week but at this stage it's a doubt."