A frustrating first half for the home side saw little created in the way of clear-cut chances. Enzo Fernández had three efforts from outside of the box while Raheem Sterling provided the brightest spark of a dull display by the Blues in the opening 45 minutes.
The Stamford Bridge crowd expected a response after the break, but they soon saw their side go a goal down when Moisés Caicedo gave away possession cheaply in a dangerous area, allowing Forest to counter. Anthony Elanga finished calmly past Robert Sánchez.
Fernandez looked most likely to make something happen when allowed to venture further forward. He looked to unlock Nicolas Jackson, who should have equalised when found by Sterling only to miss the target completely.
Malo Gusto looks to be a strong replacement for Chelsea captain Reece James, who remains out through injury, and Sterling also provided another example of how he can thrive in manager Mauricio Pochettino's system.
Chelsea struggled to create chances in a fixture where they should have been able to assert their dominance more, particularly after the number of signings they have made this summer. The Blues' performance won't instil much confidence going forward.
Another error leading to a goal from Caicedo is a habit that the Ecuador international and British-record signing needs to break as soon as possible.
Manager rating (1-10; 10 = best)
Mauricio Pochettino, 6 -- Chelsea controlled the match, with Forest's chances only coming from individual player mistakes. Pochettino was aggressive with his substitutions as he brought on attacking players, but he was let down by his team's lack of cutting edge on the day. Overall, it's difficult to blame the manager for this result.
GK Robert Sanchez, 5 -- Had little to do with Chelsea limiting the number of Forest's chances, but couldn't save Elanga's well-placed effort in the second half. Distribution could have been better.
DF Ben Chilwell, 6 -- Chelsea looked most dangerous down Chilwell's side when they found him in the attacking third, but his teammates weren't quite on the same wavelength to make the most of a number of well-placed crosses into the box. Booked for a needless foul in the first half.
DF Levi Colwill, 6 -- Didn't stand out too frequently on the left side of the back three and that is normally a positive indicator for a centre-back. Looked to break the lines when on the ball, moving it swiftly into midfield. Looked frustrated in the second half as tension began to grow around the stadium.
DF Thiago Silva, 5 - The Brazilian centre-back faced a difficult physical battle with Forest striker Taiwo Awoniyi, who was able to hold the ball up and use his power to get into dangerous positions. Had an effort in the second half from close range but couldn't guide it inside the near post.
DF Axel Disasi, 6 -- Kept things simple when called upon with a no-nonsense approach, but wasn't called into action much. An attempt from range was blocked easily when he could have looked to pass instead.
DF Malo Gusto, 6 -- An energetic display saw him provide a regular option down the right flank, while he was also quick to track back in defensive phases when little got down his side. Provided an option to get crosses into the box but couldn't find the target.
MF Conor Gallagher, 6 -- Another positive performance from Gallagher saw him active in defensive phases to win back possession, while he also helped control possession by providing a recycle option. Went close with a left-footed strike that curled over the bar.
MF Moises Caicedo, 5 -- Dispossessed too easily at times, and he gave the ball away for the counter-attack that led to Forest's winner. Substituted in the 77th minute. Not the sort of performance that convinced Chelsea to pay a record fee for him.
MF Enzo Fernandez, 6 -- Anonymous outside of a number of efforts in the first half that he really should have done better with, including one from 18 yards that he put over the bar. Began to create more in the second half with a number of progressive passes that unlocked the defence.
MF Raheem Sterling, 7 -- Always looked to make something happen with intensity that wasn't always matched by his teammates. Close to connecting with a Chilwell cross in the first half, and unfortunate not to get an assist himself when cutting the ball back for Jackson.
FW Nicolas Jackson 4 -- Shut out by the opposition for the majority of the game and couldn't find space. Struggled to find space inside the box, with his best effort blocked after an impressive pass by Fernandez. His biggest moment of the game came in the final 10 minutes when he had to do better with his strike that was sent over the bar. A massive moment in the game that he didn't take advantage of.
Substitutes (players introduced after 70 minutes get no rating)
Noni Madueke (Chilwell, 63'), 5 -- The winger tried to make things happen but faced a stubborn Forest defence. Dispossessed to the frustration of the crowd, while another effort was blocked. His best moment came when connecting with Mykhailo Mudryk inside the box, but the Ukraine international's touch was poor.
Cole Palmer (Gallagher, 62'), 6 - The debutant was quickly crowded out by defenders, which saw him slow to grow into the game, but he played a part in Chelsea's best chance of the game when playing in Sterling before Jackson's miss.
Ian Maatsen (Caicedo, 77'), N/R -- On for Caicedo for the final spell of the game.
Mykhailo Mudryk (Gusto, 77'), N/R -- Not allowed much room to express himself when introduced as Chelsea's last attacking change.