Rob Page said the game against Turkey was changed on its head by Joe Morrell's red card as a second defeat in four days leaves Wales' qualification hopes in serious peril.
Wales lost 2-0 in Samsun, which came after the 4-2 loss to Armenia on Friday, in what has been a damaging camp for his side.
But he believed that the result in Turkey might have been different if it were not for Morrell's first-half red card, after which Wales were right up against it and Turkey had goals chalked off and even a penalty saved by Danny Ward.
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Speaking about the match, Page said: "Whenever you come to Turkey away, you know it's a tough test.
"Having said that, before the sending off, I thought we matched them and I was really pleased with the performance defensively, which we obviously addressed off the back of Friday's result.
"With the ball I thought we got Aaron (Ramsey) and others in great positions up the pitch and we were brave to play through them. We looked at the footage and we thought that was an area we could exploit and that was working up until the sending off happens. Completely changes the game.
"Up until the 70th minute I thought we defended our box really well, only one cross into our own box and it cost us, that first goal."
Morrell's red was Wales' second in four days, too, after Kieffer Moore's against Armenia on Friday. Their third in six games if you go back to Wayne Hennessey in the World Cup.
Page said no one was as disappointed in the Wales changing room after the match than Morrell, whose high foot in the 41st minute caught Turkey's left-back Ferdi Kadioglu's thigh. There were no real complaints when Morrell was given his marching orders.
"He's not intentionally doing it," Page said. "He's got his eye on the ball, but when you put your foot that high, you run the risk of getting a red card. He knows it. There's nobody more disappointed than Joe in the changing room.
"I'm disappointed with Kieffer's on Friday, the goalkeeper knew exactly what he was doing. It's the softest red card, but you lift your foot and you open yourself up for a red card.
"Joe is the same tonight. He has not got it in him to hurt somebody, but you lift your foot and you're asking the question. But you've got to learn. It's frustrating, but we have to learn from it."
Page asked for a reaction from his players after the embarrassing home defeat by Armenia, and despite the defeat in Samsun, he believes his players did front up and attempt to right the wrongs from last Friday.
"I couldn't be more proud of them," he said. "I saw them in the changing room, we spoke about it in great detail the last couple of days. I asked them to go and give a performance the supporters would be proud of and until the sending off they did. Even after that, they had to put a shift in.
"The work those boys have just gone through, to go down to 10 men and continue to run themselves into the ground for me was incredible. I thought we were going to hold on to that point, but you can only sustain so much pressure."
It doesn't change the fact, though, that Wales, who are on a dismal run of one win in 12 games, now see themselves languishing in fourth position in their group at the halfway stage.
He now believes the final four games have to be treated as 'must-wins'.
"We've seen Armenia beat Latvia in the 91st minute tonight. Both teams are capable of picking points up," Page added. "There's loads of points to play for and we have got to have that mentality where we have got to win every game now.
"To give ourselves a chance, that has got to be the mentality.
"Absolutely (I still believe). To qualify, we need to get both sides of the game bang on and do it really well, if we are to be successful. It's been a frustrating camp but there have been so many lessons to learn from it. We will address it. We go into every game to win it.
"It just means it's really important we get wins at home and get as many points from them."
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