Asked on Thursday morning about Kevin Friend, the referee for the game, Lambert said: "I spoke to Kevin afterwards, and obviously what is said in there stays in there. But I didn't need to speak to him really.
"It was a clear handball.
"It's a stonewaller, a clear penalty. I don't care what anyone says, that is a penalty.
"Gabby has won the header and it has hit John's hand. I'm pretty sure if it had been down the other end, it would have been given."
Lambert and Chelsea manager Jose Mourinho were engaged in what appeared to be some heated arguments by the touchline during the contest.
But Lambert insists the technical area exchanges were predominantly "banter".
He said: "I was calm last night.
"I think there has been a lot made of me and Jose in the technical area. There was the odd little thing, but there was a lot of banter between us."
When it was put to him that Mourinho had said post-match that Lambert "complains with every decision", the 44-year-old said: "So did he. It is the same. The two of us were shouting at referees and officials and everything.
"I'm not going to go there and lie down, and neither is Jose.
"A lot has been made of me moaning - he does his fair share as well, just to let you know.
"It is not a problem. We had a bit of banter between us and I saw him afterwards. I like him and he is a brilliant football manager. There was never a problem."
- Sports & Recreation
- Jose Mourinho
- Branislav Ivanovic
- Christian Benteke
- Gabriel Agbonlahor
- Kevin Friend