Declan Rice steered home a terrific 48th-minute goal to edge West Ham past Arsenal at the London Stadium and further enhance his soaring reputation.
The 19-year-old's excellent effort capped a man-of-the-match performance against the Gunners, who had two goals chalked off for offside.
It was his first goal for West Ham, and was yet another reminder of why England and the Republic of Ireland are currently in a tug of war for his services.
Rice is expected to make a decision on which country he'll represent in the next couple of weeks. For now, he'll bask in a sweet home win over Unai Emery's polished outfit.
Arsenal began brightly and then had a flurry of chances after falling behind but West Ham were good value for the three points as they put a dent in the visitors' top-four hopes.
Former Gunners midfielder Samir Nasri, rebuilding his career at West Ham after a doping ban, was at the heart of much of the hosts' best work on his Premier League debut for the club.
It was the Frenchman's neat lay-off that allowed Rice the space to curl a superb shot past Bernd Leno.
Rice had headed wide in a first half in which West Ham took charge with Felipe Anderson drilling a shot fractionally wide of the post after another lay-off by Frenchman Nasri.
Arsenal striker Alexandre Lacazette had a double chance early on and Matteo Guendouzi's 25-metre effort flew just wide but Arsenal struggled to exert any sustained pressure.
Alex Iwobi shaved the post with a low shot but Arsenal failed to score for the first time in 21 Premier League matches. They remain fifth on 41 points while West Ham move up to eighth on 31 points before the rest of the weekend fixtures.