Alireza Jahanbakhsh's spectacular overhead kick earned Brighton a share of the points against Chelsea and dampened Frank Lampard's New Year celebrations on Wednesday as Aston Villa secured a vital win against Burnley.
Chelsea's 1-1 draw on England's south coast gave them a five-point lead over fifth-placed Manchester United in the race to secure Champions League football for next season.
Cesar Azpilicueta gave the visitors an early lead, tapping in from close range following a corner in the 10th minute but Brighton were never out of it and pulled level in the 84th minute courtesy of Jahanbakhsh's moment of magic.
"It was frustrating for different reasons," Lampard told BT Sport. "In the first half, the game was there to be won. We weren't ruthless enough. We got the goal and we had the possession. But we just didn't kill the game off.
"We allowed them to stay in the game. In the end it was a wonder goal but we were lucky not to lose the game."
The Chelsea boss said he was concerned about the lack of consistency from his side, who have beaten Tottenham and Arsenal in recent weeks but also lost at home to Southampton.
The away side dominated the opening hour of the match but were clinging on at the end with the impressive Kepa Arrizabalaga denying Neal Maupay in the closing minutes.
Christian Pulisic will rue three wasted openings that ultimately prevented Chelsea from cementing their dominance.
Lampard's team were quickly on top from the start of the match and deservedly took the lead through Azpilicueta, who finished from close range after the ball fell to him.
But Brighton enjoyed a spell of possession towards the end of the first half and Leandro Trossard tested Kepa with a powerful strike that the Chelsea goalkeeper parried.
Lampard's team were quickly into their stride after the break but Pulisic failed to make the most of his chances and was replaced by Callum Hudson-Odoi in the 66th minute.
Brighton kept battling and Kepa was forced to produce an outstanding save from Aaron Connolly in the 80th minute as the home side pushed for an equaliser.
Their persistence paid off minutes later. Lewis Dunk kept the ball alive from a corner and Iranian midfielder Jahanbakhsh acrobatically found the bottom-left corner to give his team share of the points.
Grealish inspires Villa
In the other early kick-off, Villa beat Burnley 2-1 despite seeing Jack Grealish's opening goal controversially chalked off by VAR.
Wesley put Villa ahead in the 27th minute and captain Grealish doubled his side's advantage four minutes before the break as his powerful effort found the top corner.
Chris Wood pulled a goal back for Burnley with 10 minutes to go but Villa held on to secure all three points.
"It was massive. We've only had one away win all season before this," Grealish told the BBC. "To come here, one of the hardest places in the league, it was well-deserved and well-needed."
Speaking about his goal that was ruled out, he said: "I knew it was going to be disallowed, when you see some of the decisions over the past two weeks. When you score, you have the feeling it will be disallowed. When it was I really wanted to score again and thankfully I did."
Second-placed Leicester take on Newcastle later on Wednesday, with Tottenham and Wolves, also chasing Champions League football next season, also in action.
Pep Guardiola's Manchester City are hosting Carlo Ancelotti's Everton in one of the early evening matches before Ole Gunnar Solskjaer's Manchester United kick off against Arsenal in the late match.
Runaway leaders Liverpool face Sheffield United on Thursday.