Joao Felix netted his first Chelsea goal as Graham Potter's side were held to a 1-1 draw at West Ham United in the Premier League on Saturday.
The Atletico Madrid loanee opened the scoring early at the London Stadium before former Chelsea defender Emerson drew the hosts level midway through the first half.
- Ratings: Felix 8/10 as Chelsea surrender lead
West Ham thought they had snatched a late win when Tomas Soucek scored a header with just minutes remaining but it was disallowed for offside. The result means Chelsea remain winless away from home since Oct. 16.
Felix was immediately reinstated to Graham Potter's side after serving a three-match suspension for the straight red card he received in his side's 2-1 defeat at Fulham in January and was instrumental in Chelsea's high-tempo start against West Ham, stretching the hosts' defence on multiple occasions.
"First half, we were positive and we started the game well, scored a good goal. More opportunities as well, good attacking intent. We lost a little bit of control for five to 10 minutes and then conceded which we can do better with," Chelsea boss Potter said after the match.
"Second half was probably more a reflection of where we are as a group, as a team in terms of players coming up to speed, returning from injury and players adapting to the Premier League."
Goalscorer Felix said to BT Sport: "I think we did a great game and controlled the game. They scored when we were good but that is football. We had chances to score but we go strong for the game.
"We fought for the three points but I think we are strong for the next match. I feel comfortable playing in that team. There is so much quality it is unbelievable and now we need to fight together and we have everything to do a big rest of the season."
The Portugal international looked to have opened the scoring on 10 minutes as he pounced on a mistake by Nayef Aguerd to race through and eventually tap into an empty net after his initial chip was thwarted by the face of the right post. However, the effort was ruled out after a delayed offside flag.
Felix, though, was not stifled for long and put his side ahead six minutes later. A series of Chelsea attacks culminated in record signing Enzo Fernandez floating a sumptuous ball in, which the 23-year-old met to tap home after freeing himself from Aguerd in the box.
David Moyes' side tested their luck further when Kai Havertz was found in behind by Mykhailo Mudryk and slotted beyond Lukasz Fabianski, but an offside flag and subsequent VAR check put pay to striker's ill-timed run.
Despite dominating most of the match, the visitor's lead was lost with West Ham's second effort on goal as Emerson, who signed for Moyes' side from Chelsea last summer, restored parity on 28 minutes.
Vladimir Coufal found space on the right to swing in a cross which was headed on by Jarrod Bowen, finding Emerson bearing down at the back post to scuff an effort past Kepa Arrizabalaga.
"There were a lot of emotions before the game and I score my first goal in the Premier League against Chelsea so I am very happy. Of course I have a lot of respect for them but today I think it is my day," Emerson said to BT Sport.
"It was a tough game. They played very well and we suffered a lot but it is an important point against a big team.
"When you play against the big team with a lot of quality you have to stay with high concentration for the 90 minutes. We feel it is an important point for us."
The second half petered into a scrappier contest with fewer efforts on goal. Havertz powerfully headed off target after Potter attempted to shake things up with a triple substitution.
The London Stadium erupted eight minutes from time as Soucek tapped home after Kepa spilled the ball, but Declan Rice's initial effort was deemed offside after a lengthy VAR check.
Chelsea had shouts for a penalty late in the match, claiming a handball from Soucek off Conor Gallagher's strike but it was not given.
"I thought it was a good save," Potter said on the shouts for a penalty for his side. "You need your goalkeeper sometimes to get you the points."