Monk's men were on top before Bony was dismissed in the 39th minute for receiving two yellow cards, the Ivorian's departure proving the turning point as Victor Wanyama's goal 10 minutes from time secured a 1-0 away win and lifted the visitors into second place in the table.
Bony was first booked for toppling Jose Fonte while the Saints defender was in mid-air dealing with a bouncing ball, and then saw red following a misjudged tackle on Maya Yoshida on the halfway line.
"There was no malice in it but it was reckless and you run the risk of receiving a second yellow when there's a scissor motion from behind," Monk said.
"I don't need to tell Wilfried what he's done
He was distraught in the dressing room after and annoyed with himself.
"He's a good character and personality for us, but you make mistakes at times and hopefully he'll learn from it and bounce back.
"He's very honest and held his hands up and we'll move on."
Monk acknowledged the red card changed the course of the game as his side suffered a second consecutive league defeat.
"We were so dominant in that first half
We played some great stuff and it looked as if it was only a matter of time before we were going to score," Monk said.
"We had to re-assess the situation at half-time, but the second half was always going to be difficult playing against a team who want to have the ball as well.
"But, until the 80th minute, they did not have a shot at our goal and it showed how well we controlled our shape.
"Their goal was the first time we switched off."
Southampton manager Ronald Koeman admitted his side had to be patient after Bony's sending-off handed them a one-man advantage.
"We had to be patient to create a possibility, but we scored a great goal and that was enough for three points," Koeman said.
"We didn't create a lot but we had a lot of pressure and if you keep patient then you think you will score.
"I said at half-time the worse was 0-0 and I told the players to wait for the real moments to create.
"We didn't do it that often but we did one or two times and it was enough."
Koeman felt Bony's first yellow card was harsh, but said the striker could have no dispute with the second caution and the award of a red card.
"Maybe the first one he didn't exactly mean to make that fall and was maybe a bit unlucky," the Dutchman said.
"But the second one is definitely a yellow card.
"It was a tough game against a strong Swansea side and we lost too much balls in the beginning.
"We didn't win the second ball also and it was very difficult.
"It's nice for the fans who love the Saints to see us second, but as technical staff we must keep quiet
It is a fantastic start for us but it is no time to celebrate."
Source : PA
Source: PA