Thomas Tuchel acknowledged Edouard Mendy's "huge" error cost Chelsea dearly after the 10-man Blues slipped to a demoralising 3-0 loss at Leeds United.
Mendy inexplicably allowed Brenden Aaronson to steal possession on the edge of the six-yard box and poke Leeds into a 33rd-minute lead.
Further goals from Rodrigo and Jack Harrison helped the hosts claim their first win over Chelsea since December 2002.
Kalidou Koulibaly was then sent off after picking up a second booking as Chelsea's miserable outing drew to a close. It was the defender's sixth league dismissal since the start of the 2017-18 season – more than any other player in the top five European leagues.
But it was Mendy's dismal mistake which put Chelsea on the back foot, and Tuchel did not hide his frustration with the Senegal goalkeeper after the match.
Asked whether he would discuss the incident with Mendy, Tuchel said: "He knows himself. With these kinds of mistakes, I don't think we need to speak a lot.
"He knows himself that this was a mistake and honestly, this has nothing to do with protection or no protection.
"Everybody in the world sees the mistake, it's a huge mistake in a crucial time of the match. It does not help and he's the one that is the most disappointed because it cost us a lot today."
Speaking to Sky Sports, former Manchester City and Newcastle United goalkeeper Shay Given was equally critical of Mendy's decision-making, saying: "He just has a really poor first touch and his head's a bit scrambled at that point. Worst case, kick it out for a corner, just don't do what you do.
"The only thing I would say in Edouard Mendy's defence, not too many Chelsea defenders have run into a position to receive the ball from him.
"But it's still a terrible mistake from Mendy, he knows he has to clear his lines. It's a poor, poor goal to give away."
The defeat at Elland Road represents another blow for Chelsea, who conceded a last-gasp equaliser against London rivals Tottenham in their previous match.
Leicester City defender Wesley Fofana has been strongly linked with the Blues as Tuchel bids to strengthen his defence, but the Chelsea boss insists his existing squad should be performing better.
"We need to wait. The transfer period is still open. It gets later and later and we need to focus on what we have and what we can do," Tuchel said.
"We can obviously play at a high level, but we lost track when there was no need. We were not forced to lose track. Everything was going well.
"We can win with this team in Leeds, everything was going well and we had goalscoring opportunities. It went the other way and I think it was more our fault than anyone else's credit."
While a defensive addition remains an aim, Tuchel was dismissive when asked whether Chelsea could target a new midfielder, responding: "Another midfielder? We have Jorginho, N'Golo Kante, we have Ruben Loftus-Cheek, Conor Gallagher, Mateo Kovacic.
"They [Kovacic and Kane] are injured, yes, it's a problem. But they will come back. They've not disappeared."
Chelsea host Leicester City in their next Premier League game on Saturday, having claimed four points from their three outings this season.
Real Madrid hit Twente for seven, five-star Wolfsburg also win big
Real Madrid had six different goalscorers as they trounced Twente 7-0 in the Women's Champions League on Wednesday, while Wolfsburg beat Galatasaray 5-0.
Signe Bruun opened the scoring three minutes into the Group B encounter at the Estadio Alfredo Di Stefano, then Maria Mendez's header gave Madrid a 2-0 half-time lead.
Madrid, who had won one and lost one of their opening two games in the tournament, got a third through Naomie Feller five minutes into the second half, then Caroline Weir made it 4-0 with a brilliant free-kick.
Mendez headed home her second of the encounter shortly after the hour mark, while Oihane Hernandez and Carla Camacho got on the scoresheet late on to complete the rout.
The victory took Madrid second in the Group B standings ahead of Chelsea's trip to Celtic.
Wolfsburg were also convincing victors in Group A, getting off the mark for this season's competition as Rebecka Blomqvist scored a hat-trick in their 5-0 thrashing of Galatasaray.
The Bundesliga side – who failed to pick up a point or score a goal in their opening two matches – had a narrow 1-0 lead at half-time through Joelle Wedemeyer, before Blomqvist took centre-stage in the second period.
She tapped home after Janina Minge struck the crossbar, then added her second goal in the 77th minute and her third six minutes into stoppage time.
Vivien Endemann powered home a fifth for Wolfsburg one minute later, as they provisionally moved within three points of Lyon and Roma ahead of their meeting.
Taylor pleased with City's physical test during Hammarby win
Manchester City head coach Gareth Taylor was pleased with how his team stood up to the physical challenge of Hammarby in their 2-0 Champions League victory on Tuesday.
City's win extended their unbeaten start to the season, having won every game in all competitions following a 2-2 draw against Arsenal on opening day.
“Difficult game for us, physical challenge, a physical team in Hammarby. I think they outnumber us a little bit in terms of size, considering when you look at our midfield. But I thought the girls handled it really well," Taylor said after the game
“I thought we dominated the game. In the early parts we were just a little bit off in our final action. We just needed to speed up a little bit in terms of being on the end of it, and we spoke about that at half-time, and we score with Laura getting into that type of position we’d been talking about.
“[The physicality was something] we were prepared for, but dealing with it is a different thing. Having Bunny [Khadija Shaw] and Alanna [Kennedy] on the pitch, two of our more physical players, is really important, particularly for set-plays.
“At 1-0 we were defending a couple of scenarios like that, Yama [Ayaka Yamashita] making a really good save at one point. Then Aoba [Fujino] got the goal that maybe allowed us to change things up a little bit more, get some people off that we’d like to manage.
“I think the girls have dealt with it really well tonight. We expected it, we thought it would be difficult, and they rose to the challenge.”
The victory leaves City top of their Champions League group with a 100% record after three matches, three points above second-placed Barcelona.
Taylor had made changes to City's starting XI, with Lauren Hemp among the trio to drop out from the weekend and she did not feature in the squad. Ahead of their weekend game against Chelsea, who are second in the WSL, Taylor explained the reasoning behind Hemp's absence.
“We’ve just got an issue with Lauren that we just need to analyse a little bit further, that’s all," he said.
“It’s something that potentially happened in the Palace game [on 3 November]. She was able to play in the Tottenham game [last Friday] but wasn’t able to tonight, so we’ll just take a little bit longer to assess and find out more.
“Hopefully [she can play against Chelsea]. There’s an opportunity there, we’ll just have to take a moment tomorrow, have a good conversation and find out where we’re at with the medical staff.”
Forest taught 'a lesson' as winning run ended by Newcastle according to Nuno
Nuno Espirito Santo acknowledged Nottingham Forest were taught "a lesson" by Newcastle United, even if he did not criticise his side following a 3-1 defeat at the City Ground.
Forest had won their previous three matches to climb to third in the Premier League, and Murillo's opener had them on course for another victory.
But that goal came against the run of play, and Newcastle continued to dominate, eventually equalising through Alexander Isak.
Forest, who have been so solid at the back this season, went chasing victory and were instead caught out as both Joelinton and Harvey Barnes scored on the break.
Those counter-attacks have been a large part of Forest's own attacking identity previously, and Nuno was full of praise for how ruthlessly Newcastle executed that tactic.
"I cannot say that was a bad performance, that is totally out of the question," the Forest boss told BBC Sport.
"We played against a very good team that was able to control us and then hurt us in the way we've been doing. It is a lesson for us to learn.
"I just have to recognise that today we played a good team, who were better than us in many, many moments.
"There's nothing to say about the [Forest] players. The character and belief was there."
Newcastle were a little unfortunate to trail at half-time, having had seven shots to Forest's three and 60% of the possession.
Yet Eddie Howe, the Newcastle coach, still saw plenty of room for improvement, which his side delivered on after the restart.
"It was difficult, but we knew it would be," he said. "They are a difficult team to play against because they don't concede many chances and you're left fearing the worst when you go behind.
"We had work to do at half-time, but credit to the players because the second half was up there with our best performances this season.
"Everything we didn't do in the first half, we did at the start of the second half. We were intense and direct with our attacking. We asked more questions and could have scored.
"I'm really pleased with the second half."
Newcastle have won three in a row in all competitions for the first time in over a year, helped by a return to form for their attacking stars.
Isak had netted only once this season before scoring in the past four successive matches, while Barnes again showed his quality from the bench. Six of his nine Newcastle goals have come as a substitute.
Howe added: "We need our attacking players to contribute goals, and Alex has done that in the past few weeks with massive moments, then Joelinton and Harvey Barnes pop up with moments, too.
"We know we have players who can make that difference, and I'm really pleased with that side of our game.
"Harvey Barnes did what he does. He's an outstanding player. Trying to find room for him in the team is something that I am conscious of.
"I'm really pleased he got that goal – I thought it was a fantastic finish."
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