Swansea boss Paul Clement felt the referee was wrong to book Ki Sung-yueng for diving in their 4-0 defeat to Arsenal.
The Gunners struggled for inspiration in the opening 40 minutes as the hosts stifled the title chasers, but Olivier Giroud's finish from close range just before the break was a turning point in the game.
However, Swansea thought they had won a penalty just after Giroud's goal when Ki hit the deck under a challenge from Laurent Koscielny, but the Swansea man was booked for diving by Mike Jones instead.
Clement felt the referee got the decision wrong.
"We had a massive shout for a penalty - I thought the referee had given it at first," he said.
"Ki said to me at half-time that it was a penalty, although he was booked for diving. I’ve had the luxury of looking back at it a couple of times and it looks like there is contact and it should’ve been.
"It possibly could have made a big difference but I said to the players at half-time that we were in the game. We’ve got to keep going and tidy up the defensive part of the game and be more confident. We’ve got to show more personality in possession."
For the first half Swansea fought tenaciously and stopped Arsenal having a meaningful sight of their goal.
Clement was pleased with how his team approached the game in the first-half but pinpointed the ball breaking to Giroud in the area for his goal as a key moment in the match.
"I thought we were in the game in the first half and we produced some good football," he said.
"I thought generally our defensive shape was sound - their best moments came from a counter attack and got a little bit of luck that led to that massive opportunity."