The Hammers are through to a European club competition final for the first time in almost a half century.
Browsing: AZ Alkmaar
The Premier League side are now in a strong position to reach a first European final since 1976 as they head to the AZ Stadium in Alkmaar for the return next Thursday.
The Dutch side were under pressure for the whole game as Napoli dominated possession and peppered their goal.
Mason Greenwood scored his third goal in three days to rescue a point for Manchester United at Old Trafford, as Everton interim manager Duncan Ferguson remains unbeaten.
Dusan Tadic scored twice as Ajax Amsterdam all but claimed the Dutch league title with a 4-1 victory over Utrecht on Sunday as championship rivals PSV Eindhoven slipped to a surprise 0-1 loss at AZ Alkmaar.