Arthur Masuaku said he was as surprised as everyone else when his misdirected late cross beat Chelsea keeper Edouard Mendy to earn West Ham victory over the Premier League leaders in a pulsating encounter at London Stadium.
After collecting the ball wide on the left with three minutes remaining, Masuaku's attempted delivery took Mendy by surprise and flew in at the near post to spark jubilant scenes among Hammers supporters.
The win consolidated West Ham's place in the top four and means they have now beaten Chelsea and Liverpool, two of the three teams above them this season.
"So, was it a cross or was it shot?" Masuaku said on Twitter. "(Hint: I was as surprised as you)."
"I said to him I thought it was a great cross," West Ham manager David Moyes joked of the defender's first Premier League goal.
"It was very fortunate but in football, you need a bit of fortune sometimes. In the last few games we have lost it a little bit, but today we got it back."
Thiago Silva broke the deadlock for Chelsea in the first half, heading Mason Mount's corner past Lukasz Fabianski via the inside of the post.
West Ham equalised when Mendy brought down Jarrod Bowen following a poor backpass from Jorginho, allowing Manuel Lanzini to stroke home from the penalty spot.
Chelsea regained their advantage in spectacular fashion, Mount sending a superb side-footed volley into the corner from Hakim Ziyech's low cross for his second goal in two games.
Bowen's low drive from the edge of the area restored parity once more before Masuaku's remarkable late winner.
The defeat means Chelsea will drop to third if Manchester City and Liverpool win this weekend.
"This is a goal that OK, happens," said Blues boss Thomas Tuchel. "There are no mistakes, just a freak goal - the problem is that it is the winner.
"Overall we did too many individual mistakes. If you do this for three consecutive games you cannot expect always to get a result.
"The schedule we play and effort we play, sometimes you feel tired, but you just need to accept it and control our risk management.
"We hate to lose and we have to digest it now. It is not a performance to be mad about, but in detail we need to be better again.
"If we won the game nobody would have given us the title and if we lose it I don't think anybody else gets it this weekend."