The visitors took an early lead before falling behind by the break and only levelled midway through the second half.
Lambert said: "I thought we were excellent in the second half.
"We started the game well but they penned us in after we scored and we never got going after that.
"We got them in at half-time and we regrouped. I would have smashed some tea cups but we weren't given any.
"I wasn't happy and they knew that but we were excellent in the second half.
"We could have won it in the end. I'm disappointed not to win but performance wise we were spot on.
"It could be a huge point for us. We still haven't lost two in a row which is an incredible achievement and shows our desire not to get beat."
He added: "While I'm here dropping out of the top two won't affect the players. There is a lot of football still to be played and I'm relishing it.
"The achievement of these lads is already incredible. Nobody expected us to be where we are and we have been terrific.
Watford boss Malky Mackay was surprised that Grant Holt had not been sent off.
He said: "Both sides had chances so the neutral will go away happy.
"At 2-1 up we missed an open goal when Danny Graham missed the ball and if that went in for me the game was dead. But overall I'm very proud of them.
"We shot ourselves in the foot in the first minute but we came back strongly.
"Grant Holt was booked for persistent fouling and then had five other fouls after that.
"With certain centre forwards part of their game is to be bustling and dominate opposition defenders and Grant is one of them. He's a good player but it's remarkable that there was no further action taken against him.
"The referee will be disappointed that his actions weren't different and it changes the game.
"To be fair, he played a good advantage for our second goal but it was incredible that he didn't then go back and book Zak Whitbread. It was great inconsistency."