The Reading captain, who was already on a yellow card, made a late bodycheck onto the former Exeter man but escaped censure from the match official.
Watkins felt that McShane was lucky to stay on the pitch but refused to use that as an excuse for the Bees failing to win.
“One of their lads (Paul McShane) was lucky not to get sent off in the first half, but we can't make excuses - we have to pick ourselves up and go again,” he said.
“He took me out in the first half, then another body check. But that's football - sometimes it goes your way and sometimes it doesn't.”
Brentford had led through Josh Clarke's fine finish on 15 minutes but their hopes of a first Championship win were ended, despite missing chances to put the game to bed, when Rico Henry's foul on Liam Moore in the box allowed Liam Kelly to drive home an equaliser from the penalty spot.
The 21-year-old admitted it was a mix of frustration at not winning but taking confidence from another good performance.
Watkins added: “It's a bit of both really, because we're playing well but it's down to ourselves to put the ball in the back of the net.
“It's frustration as well, because we're playing well against these top teams and we're not punishing them.”
He explained further: “We're creating chances and we're playing well, you switch off for a split second and you can see that anyone can beat anyone.
“They're a good team, they were up there last year and in the playoff final, and we showed today what we can do - we can play well against anyone.”