Brentford boss Dean Smith was proud of his players but critical of referee Christopher Kavanagh after the Bees got nothing from a game they dominated for long spells.
Deep into nine minutes of injury time, big striker Philipp Hofmann was hauled back in the box but play was waved on.
"Normal service was resumed as far as penalties are concerned," said Smith.
"I watched it back and Hoff is going to head the ball and their guy is going away from goal with a fistful of his shirt, so how it's not a penalty I don't know."
Smith felt Brentford's goalscorer Lasse Vibe also had a strong claim for a spot-kick late on.
The home boss explained why he opted to leave £15million-rated West Ham and Watford transfer target Scott Hogan on the bench.
"I made the decision on Thursday not to play Scott and felt that Romaine Sawyers and Lasse Vibe did well last week. It is very difficult for him and I decided not to start him in the long-term interests of the football club," said Smith.
"The long-term interests of the club always have to be at the forefront of my mind. I didn't think it was right to start him and Scott didn't either."
Despite the defeat, Smith was delighted with the performance of his side: "We gave a great account of ourselves and were unfortunate not to win the game let alone get a point.
"We didn't start well in the first five or 10 minutes and then only Dwight Gayle can score a goal like that in the Championship, but after they scored I thought we dominated the game."
He added: "In the second half we played with a lot of confidence and to see a side like Newcastle, and all the resources available to them, hanging on for the last 20 minutes is a great credit to our players."