Neil Baker and Jon Underwood sprang something of a surprise with a full debut for 18-year-old striker Alfonso Tenconi - and he almost opened the scoring in the very first minute, but fired straight at Will Mannion.
The Rebels took the lead on 10 minutes from a corner as Freddie Grant met a corner kick with a powerful header which beat Mannion and found the top corner.
Just eight minutes later Slough doubled their lead thanks to a goal from the penalty spot. Ben Harris was brought down inside the Hawks box and Aaron Kuhl converted from the spot, slotting his kick into the bottom right hand corner.
The Rebels’ dominance forced the hosts into a change of personnel and shape, with striker Scott Rendell replacing Manny Adebowale.
Just before the half time whistle Kuhl almost got his second for the day, but skied the ball over the crossbar.
Slough took a two-goal lead into the break, and around the 56th minute mark Havant almost pulled one back as Jonathan North punched a corner kick out for a corner.
Havant struggled to create many chances for most of the second half thanks to Slough’s superb defending. The only notable chance before the final 15 minutes was well saved by North after a 20 yard volley from James Roberts.
With 10 minutes to go Havant’s Tommy Wright was shown a straight red card for a foul on Jonathan North. After a through ball was played forward, Wright went in and was adjudged to have caught the goalkeeper with his boot.
A massive ten minutes was signalled for added time and it was a very nervy conclusion for the Rebels as in the fourth minute they conceded a goal from a cross, with McCarthy heading past North.
Then only two minutes later, Sean Fraser saved the day for the Rebels as he managed to make a fantastic block on the goal line from a powerful strike following a corner kick.
Slough held on to claim all three points and will be hoping that this victory kickstarts their season, with the visit of Bath City to Arbour Park on Tuesday evening.
Havant & Waterlooville Line up
Mannion, Passley (Green 80), Oastler (c), Magri, Adebowale (Rendell 25), Newton, Rooney (Baggie HT), McCarthy, Clifford, Roberts, Wright. Unused substitutes: Searle, Collins.