Steve McClaren felt referee Mike Jones could have been more “lenient” before showing Daryl Janmaat a second yellow but admits it cost his side.
The Dutch full-back was given his marching orders just before half-time at the Liberty Stadium, with Newcastle trailing 1-0 to a Bafe Gomis 9th minute goal.
It didn’t get any better for the visitors after the break with Andre Anyew - a summer target of Newcastle’s - adding a second to seal the 2-0 win
The game was effectively over from that point, with Newcastle struggling against a rampant Swans side.
Janmaat had been booked earlier for a foul on Jefferson Montero before pulling the impressive winger back, 70-yards from his own goal.
McClaren said: “I thought it was harsh, it was a long way from goal.
“Okay, Daryl had made his presence known, which he needed to do.
“It was a little tug. I think the referee could have been more lenient.
“From then on, it was very difficult.”
He added players showing “emotional control” was the only lesson his side could learn from the defeat at Swansea.
McClaren added: “I think the first one [Janmaat booking], you could see the referee had made his intentions clear.
“If we learn anything, it is emotional control.
“That has cost us, that is the only lesson we can learn - keeping 11 players on the pitch.”
Siem De Jong missed the game with a shin problem, which flared up.
Moussa Sissoko was taken off with a groin strain at half-time and will be assessed, confirmed McClaren.