Tomas Soucek and Jarrod Bowen both struck inside five second-half minutes to secure West Ham a 2-0 victory over Crystal Palace at Selhurst Park.
Soucek finally broke the deadlock in the 67th minute before Bowen made it two on a south London afternoon that started under soggy conditions.
Eberechi Eze had produced the best chance for either side before the break with a crossbar-rattling effort that appeared to have swung momentum the hosts' way.
Substitute Ismaila Sarr nearly cut the deficit but like his team-mate was denied by the woodwork as the hosts walked away empty-handed on his home debut.
Oliver Glasner's Palace squad had shrunk by two over the previous 24 hours after Joachim Andersen and Jordan Ayew's respective moves to Fulham and Leicester were finalised.
Chadi Riad was handed his Premier League debut in the absence of the departed Dane, while Julen Lopetegui's line-up was unchanged from the Hammers' season-opening loss to Aston Villa.
It was West Ham who got off to the brighter start with headers for Soucek and Michail Antonio both off target, before Eze's effort took a dangerous deflection off Vladimir Coufal, landing on the roof of the visitors' net.
Max Kilman was next to have a go with a nodded effort, while Mohammed Kudus came up just short of an opener after he pounced on a loose ball and directed his attempt just wide of Dean Henderson's left post.
Palace began to grow into the game, Alphonse Areola denying Eze his first goal of the season with an outstretched leg, while Odsonne Edouard should perhaps have fired the hosts into the lead after outpacing his marker but dragged his attempt just wide of the far post.
The rain finally relented but, while the pace remained quick, clear-cut chances were hard to come by until Eze rattled an effort off the crossbar three minutes from time, the closest either side had come to an opener.
Edouard rolled a shot straight at Areola soon after the restart following an intervention from Eze to win possession at the edge of the area, while the visitors did well to thwart the hosts' extended stay in their final third.
Both bosses rang the changes in the 63rd minute, Glasner introducing summer signing Daichi Kamada and Lopetegui bringing on Aaron Wan-Bissaka.
The Hammers took the lead four minutes later, a goal facilitated by some initial work from former Palace man Wan-Bissaka before the ball eventually found its way to Soucek, who finished into the bottom left corner.
There was a brief pause as a result of the subsequent celebrations in the away end, where the travelling support surged forward with such force that they brought down the hoarding in front of them.
Their side doubled their advantage five minutes after the opener, Kilman sending Bowen through for a left-footed strike in the 72nd minute.
Sarr had just come on for Edouard but the Senegal international's Selhurst Park introduction did not play out the way he wanted after his cross skipped by Jean-Philippe Mateta in striking range.
Sarr was inches away from clawing one back but his attempt to deflect Tyrick Mitchell's cross with his hip pinged off the post.
