Two early goals gave Haslemere the best possible start in this local derby, but they were unable to sustain it and in the end were comprehensively beaten by their old rivals.
Hammer were punished for their very lethargic start, Simon Bryan and Andrew Hibberd scoring opporunist goals inside the first 10 minutes.
It was 20 minutes before the home side started to impose themselves and they reduced the arrears when Ramy Salameh drilled home a fine left-foot shot.
United now took a firm grip on the game and equalised on the half-hour with an excellent goal. Dean Woods broke down the left before chipping a clever ball into the goalmouth where skipper Jeff Cox rose high to head past Jym Clement.
Hammer maintained the pressure and took the lead when leading striker Robbie Stewart blasted the ball home from some 20 yards.
The second half started disastrously for Haslemere. From the kick-off, Hammer sped downfield; Stewart's shot was blocked on the goal line and, in attempting to clear, a defender put the ball in his own net.
With a comfortable 4-2 lead, Hammer took their foot off the pedal, but Haslemere's twin strike force of Rob Chalcraft and Simon White could made little headway against the redoubtable Tony Wright and Danny Wilding in central defence.
The last 15 minutes saw an improvement by Hammer and two very good goals. Cox's superb diagonal ball split the Haslemere defence and was picked up by Neil Robb, who cut inside and gave Clement no chance with a crisp shot.
Despite the sterling efforts of Bob Daynes and Kev Toomey, Haslemere were now in some disarray and the rout was completed when Carl Thayre's splendid free-kick shot sailed into the back of the net.