Goalkeeper David Martin was “in tears” after a debut where West Ham ended a seven-game winless run with victory at Chelsea.
Martin, the son of Hammers legend Alvin, was picked by boss Manuel Pellegrini instead of Spanish keeper Roberto, who had conceded nine goal in three games.
And it proved an inspired choice as the visitors kept a first clean sheet since 22 September and achieved a first victory at Chelsea for 17 years.
Aaron Cresswell scored the winner three minutes after the break as he cut inside and fired low past Kepa Arrizabalaga.
Chelsea had plenty of chances early on as Christian Pulisic missed the target from a few yards out. The American also wasted a great opportunity late on.
But West Ham relieved the pressure on Pellegrini as 33-year-old Martin also made it a Premier League debut to remember.
The former Millwall and MK Dons keeper sank to his knees before celebrating in the stands with his father, who played in the West Ham defence for 21 years.
“It still doesn’t feel real,” said Martin, who is a boyhood fan. “I’m just pleased I got through it, I didn’t let anyone down and actually I enjoyed it in the end.
“My dad didn’t say much – I think we were both in tears. For my dad to play for the club for 21 years and see it, and for me to make my debut, keep a clean sheet and get win for the boys, it is so pleasing.
“I was struggling to eat for two days; Cressa [Cresswell] was laughing at me because my plate was taken away because I couldn’t eat my food.
“I hope I’ve given myself a good chance [to keep my place] but I have to work hard and keep grounded.”
Victory lifted West Ham four points clear of the relegation zone while Chelsea failed to close the three-point gap to second-placed Manchester City and Leicester City in third.
Chelsea pay for profligacy
Although West Ham held firm, Chelsea paid for failing to take their chances with Pulisic perhaps the most guilty after lifting an effort over early on and slicing a chance wide after being put through by substitute N’Golo Kante.
To blame Pulisic, who has scored five goals in his last four Premier League games, would be unfair, though. He was among Chelsea’s best players as he attacked from the left, with Reece James also showing plenty of endeavour down the right.
Manager Frank Lampard, who had a stellar record against former team West Ham while playing for Chelsea, was missing top scorer Tammy Abraham, who injured his hip in the 2-2 draw at Valencia in the Champions League in midweek.
The Chelsea boss also made several changes as Kante started on the bench, and Mason Mount came back into the side where he battled against best friend Declan Rice in midfield.
But after the first 25 minutes where they were in the ascendancy, the game changed course after Arrizabalaga saved well from Antonio’s header.
The visitors grew in confidence from that chance and Chelsea struggled to contain their counter-attacks which eventually led to Cresswell’s goal.
Without the more mobile Abraham, Chelsea found their best chance came from the wings, but Giroud was poor and Mount was not clinical when he was presented with a sight of goal.
Willian came on to provide a boost towards the end, but Chelsea showed once again that when they cannot score, teams can find a soft core in their defence.
They have now conceded 20 goals in their 14 Premier League games, and following six successive wins, they have now suffered back-to-back defeats following last Saturday’s loss at Manchester City.