Newcastle manager Rafa Benitez had plenty to smile about but the result did not make happy reading for the Hammers, who suffered a third defeat in as many opening league games for the first time since the 2010-11 season, when they were relegated.
Former Liverpool and Chelsea manager Benitez, who also celebrated a milestone of 500 Premier League points, praised the fans as well as Joselu and midfielder Matt Ritchie after seeing the Magpies brush aside the visitors.
"The fans were crucial last year (when Newcastle were in the Championship) and they have to be crucial this year - they are trying to help," Benitez told the BBC.
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"I think I have some friends in the stands. I said before that Joselu needed to be fit. He did well, it was a great effort, we understand we will need everyone for the whole season.
"Matt Ritchie is an important player, the way he works is an example for the others."
Joselu, who made his first start for Newcastle after joining them during the close-season from Deportivo La Coruna where he played on loan from Stoke City, fired Newcastle ahead with a 36th-minute goal of the highest quality.
He capped a fine move as midfielder Mikel Merino released Christian Atsu and the Ghana winger squared the ball into the heart of the penalty area for Joselu to sweep home.
West Ham and England keeper Joe Hart produced several fine saves after the break to keep the visitors in the match but was powerless when Clark headed in a superb Matt Ritchie cross from the right in the 73rd minute to make it 2-0.
Late substitute Mitrovic was denied by Hart with his first touch of the ball before he put the icing on the cake when he rounded the keeper and stroked the ball into an empty net.
(Writing by Zoran Milosavljevic; Editing by Neville Dalton and Ed Osmond)
