Snodgrass curled in a fine cross from the right and Hernandez ran behind a static defence to finish from close range.
The Mexico forward was more clinical six minutes later as he latched on to an Arnautovic flick-on and beat Martin Dubravka at his near post with a precise finish.
Perez dragged a shot wide later in the half while Salomon Rondon saw an effort brilliantly blocked by a sliding Pablo Zabaleta.
Javier Hernandez proved to be the difference between the two sides at St. James' Park as his brace earned West Ham their first win in nearly a month, the Mexican showing good movement for his first of the game, while his composed finish sealed the win for the Hammers.
What does it mean?
Andy Carroll took has done full training during the course of the week and like Wilshere, he too is expected to start the Newcastle vs West Ham game on the bench.More news: NASA, Russia launch Soyuz rocket to ISS just weeks after failure
Manuel Pellegrini gives his team instructions during the match with Newcastle United. The Austria global found space time and time again in the first half and was also at the heart of West Ham's best efforts on the counter-attack prior to his 70th-minute withdrawal.
West Ham defender signed for £22million (BBC) in the summer from Toulouse and he looks like an incredible investment for the club.
The result, wrapped up with a late goal from Felipe Anderson, lifted West Ham to 13th place on 15 points from 14 games and ended Newcastle's three-match winning streak as the Magpies, who have 12 points, slipped to 14th.
- West Ham recorded their biggest Premier League victory against Newcastle at St James' Park since October 1998 (also 3-0).
Is this, finally, the fabled new West...
- West Ham's Felipe Anderson has scored four goals in his last four Premier League games having netted just one in his opening 10 appearances in the competition for the Hammers.
West Ham's fast breaks had toothless Newcastle reeling all afternoon and livewire Mexico global Hernandez fired them ahead in the 11th minute with a sweeping close-range finish after a fine cross by Robert Snodgrass. "We scored three and could have got more".