West Ham's £36million recruit Felipe Anderson - who scored the visitors' third goal - was outstanding in the game. "The difference between teams is not too much, but, in general, the league is tough".
Snodgrass curled in a fine cross from the right and Hernandez ran behind a static defence to finish from close range.
Newcastle did have chances to equalise before the break, with Ayoze Perez failing convert any of the four that came his way, while Salomon Rondon had a shot blocked well by Pablo Zabaleta on the stroke on half time. Over their last four games, West Ham have picked up five points.
Arnautovic superbly headed down a lofted West Ham clearance into Hernandez's stride and the 30-year old made no mistake as he drove the ball past Newcastle goalkeeper Martin Dubravka inside the near post.
Marko Arnautovic's intelligent movement repeatedly caused problems as Newcastle's defending remained unconvincing, although West Ham were unable to muster another effort on goal in the first half.
Newcastle looked to have been building some momentum prior to that strike, but rarely threatened thereafter and Felipe Anderson made it 3-0 when he took a pass from fit-again substitute Jack Wilshere, rode a challenge from Fabian Schar and nutmegged Dubravka.
Hernandez will get the headlines, but Arnautovic was similarly impressive in attack for West Ham.
"I can not complain of the effort of the players or the commitment but again today we had chances, but they scored theirs". On Saturday, the Magpies welcome West Ham to St. James' Park, with one team looking to move ahead of the other in the table. The Magpies will look to extend their winning streak to four games against West Ham.
West Ham's fast breaks had toothless Newcastle reeling all afternoon and livewire Mexico worldwide Hernandez fired them ahead in the 11th minute with a sweeping close-range finish after a fine cross by Robert Snodgrass.
- West Ham have kept their first away clean sheet of the season and their first on the road in the competition since their final away game of the 2017-18 campaign against Leicester (2-0).