The home side had a 37th-minute Dylan McGowan effort ruled out after assistant referee Francis Andrews flagged for a foul by Jason Holt on United goalkeeper Radoslaw Cierzniak.
The Polish shot-stopper had appeared to misjudge Callum Paterson's long throw, leaving the Australian defender with a tap-in.
McNamara said: "I thought it was a free-kick (for Hearts' disallowed goal).
"I watched it back. I know it's soft but it's still a free-kick. The lad went into him first as he's thrown the ball and he's gone in again to put him back towards to his goal. It's a foul. Nadir's one for the foul against Goody, I thought he just used his body there.
"I thought there was not much in that. I know Lockie (Gary Locke) is a bit frustrated with their goal but it was a foul."