During a cagey opening 10 minutes, Edon Pruti headed a glorious opportunity straight at Ross Worner in goal after being found by Johnny Goddard on the left, but the flag was raised by the linesman.
Despite a slow start by both sides in the sweltering heat, James McCarthy unleashed a red-hot finish leaving Jonathan North stranded in goal in the 20th minute.
McCarthy sublimely connected with a deflected ball in the air and volleyed extraordinarily into the top right corner of the net to open the scoring.
After the interval, it only took six minutes for the Hawks to double their advantage. James Roberts slotted underneath North from inside the area, after good work from Gianni Crichlow to feed the winger.
The Rebels had struggled to assert pressure throughout the game, but on 60 minutes they pulled a goal back.
Johnny Goddard stepped over a free kick on the right-hand side which Ben Harris leapt highest to meet and crash a header off the underside of the bar and into the net, sending the travelling contingent wild behind the goal.
Harris almost turned provider on 67 minutes, after his searching cross on the right was diverted inches over his own crossbar by Havant defender Joe Oastler.
On 78, the hosts extended their advantage once more to dent any hopes of a late comeback from Slough.
The lively Crichlow dinked a perfect ball over the Rebels defence to find Paul Rooney in acres of space, who headed into the back of the net with ease.
The damage could have been worse as North was sent sprawling across his box to deny a header from close range.
North had a busy afternoon between the sticks with his feet denying Hawks substitute Muhammadu Faal after racing beyond the Slough backline.
A disappointing start to the season for Slough, and they will look to get points on the board at Arbour Park next week against Tonbridge Angels.
Havant & Waterlooville Line up
Worner, Newton, Oastler, Nembhard, McCarthy, Rooney, Prior (Wright 81), Clifford, Crichlow, Read (Passley 69), Roberts (Faal 69). Unused substitutes: Gobern, Andrews.