Sam Allardyce was "convinced" his side should have had a second penalty after being denied victory in his first game as Crystal Palace manager.
Troy Deeney's 100th strike for Watford earned a share of the points after Yohan Cabaye's opener, but Christian Benteke missed from the spot before Wilfried Zaha was booked for diving inside the area.
Mark Clattenburg's decision on Zaha caused frustration for Allardyce, who said his Palace side deserved better from the game having turned in an improved performance.
Allardyce, who replaced Alan Pardew just before Christmas, told Sky Sports: "I looked at all the incidents and there is no doubt in my mind. It's a penalty for me, but maybe [Clattenburg] didn't want to give three [penalties] today.
"I'm a little disappointed in the decision process from one of the best referees in the world today."
However, despite the disappointment, Allardyce was encouraged by the display.
"In terms of results we played very, very well today and it's our own fault we didn't get the three points," he said.
"We got a little deflated at missing the penalty, but we were the dominant side until then."
He added: "If we can stay on that level hopefully we'll turn results into victories. I was looking for the important clean sheet and today we gave that up by giving them a soft penalty."
After putting away the "soft" penalty, Deeney finally brought up his century for the Hornets, something he admitted had been playing on his mind.
He said: "It's nice to finally get it done. I've been having a bit of a stinker recently so it's a huge weight off my shoulders. It's one of those that when I retire I'll look back on how nice it is, but I've got to get 105 now to get to fourth place [in the club standings]."