Daryl Janmaat has admitted his "stupid" actions cost Newcastle any chance of success at Swansea.
Newcastle slipped to a timid 2-0 Barclays Premier League defeat with Janmaat sent off before half-time for two bookable offences.
The Dutch defender was booked after twice fouling Jefferson Montero and banished four minutes before the break for pulling back the Ecuadorian winger deep inside the Swansea half.
Newcastle manager Steve McClaren called it a "harsh" decision and felt referee Mike Jones should have shown leniency, but Janmaat was remorseful and apologised to his team-mates and the club's supporters for his red card.
"It was stupid of me and I have to apologise to my team-mates, the supporters and everybody, because trying to win a game with 10 men is very difficult," Janmaat told nufc.co.uk.
"The first yellow card was clear. The second one, I lost the ball, he (Montero) ran past me and in a split-second I touched him.
"I pulled him back and that was stupid.
"With 11 men at Swansea it is already hard but with 10 men it makes it almost impossible. We didn't give up though, and the rest of the team gave it everything, but it was a disappointing game."
Janmaat's actions provoked a spat between McClaren and his Swansea counterpart Garry Monk, who accused Newcastle of trying to stop the in-form Montero with a tactic to "basically try and kick him".
McClaren rejected that accusation by saying his team are "not capable of doing that" but it was a damage limitation exercise for Newcastle after Andre Ayew had added to Bafetimbi Gomis' early opener within seven minutes of the restart.
Ayew now has two goals in two games since his summer move from Marseille and the Ghana forward appears to have made a seamless transition into English football.
"He (Ayew) has contributed fantastic and I thought he played exceptionally well," Monk said.
"I brought him off because I thought at that point the ref was giving out some yellow cards quite cheaply and I didn't want any risk of it being evened up.
"But the whole team contributed and I was very pleased with the performance.
"I don't think the sending-off mattered as we dominated from start to finish, we were clinical and defended well again with a clean sheet."
Swansea started their season with a 2-2 draw away to champions Chelsea and have had a player sent off against them in each game.
"The Premier League is physical and ferocious at times and you have to be able to stand up to it," Monk said.
"My players have shown we can handle that side of it and we can give it ourselves as well, which is important, but we try to play football."