The Black Cats went on the front foot from the very beginning, with Noah Sadiki’s shot from the edge of the box working Alphonse Areola inside 90 seconds.
Even so, the hosts were able to work some possession and took the lead in the 14th minute when Jarrod Bowen got to the byline and delivered a cross that hung up in the air for Crysencio Summerville to rise above Nordi Mukiele and head home.
A chance was squandered at either end shortly after, as Trai Hume looped a header onto the roof of the net before Pablo blazed his effort off-target.
The visitors came close again with Dan Ballard heading wide, but they suffered yet another blow before the half-hour mark, with Ollie Scarles luring Hume into a challenge to concede a penalty that Bowen clinically converted with a pinpoint effort past Robin Roefs, who had dived the right way.
The excitement around the London Stadium was palpable following the second, and Taty Castellanos saw a header saved before Summerville’s attempt was deflected behind.
The hosts then had even more reason to celebrate before the break, as Mateus Fernandes hit an outrageous strike into the top corner despite Roefs getting a hand to it.
West Ham continued to look confident after the restart, but the Black Cats also competed with Habib Diarra seeing a shot blocked by Jean-Clair Todibo, having been introduced as one of three half-time changes from Regis Le Bris.
After Castellanos hit a curling shot that was routinely saved, Sunderland struck back in the 66th minute with Mukiele providing a pinpoint cross that Brian Brobbey headed inside the post.
After looking so comfortable, the Hammers were now being subjected to increasing pressure, but Wilson Isidor smashed his volley over when an opportunity arose.
Areola then had to produce a superb save to stop Luke Onien’s cross-turned-shot, ensuring that West Ham recorded back-to-back PL wins, having not been victorious in any of their previous 10 league matches. Victory takes the Hammers two points behind 17th-placed Nottingham Forest ahead of their match against Brentford. They also inflicted the second defeat in Sunderland’s last three PL matches.
Flashscore Man of the Match: Mateus Fernandes (West Ham United)