Watene-Zelezniak had a try disallowed in the 11th minute off a crossfield kick from five-eighth Jamie Soward before crossing the line five minutes later after good work by centre Jamal Idris.
Mansour crossed just before the break from a superb cut-out pass by Soward for an 8-0 advantage.
The Raiders opened their account in the 55th minute when forward Paul Vaughan dived over the line after smart support play by five-eighth Jack Wighton and fullback Anthony Milford and, with Jarrod Croker's successful conversion, the visitors were down 8-6 and poised to steal victory.
But a crossfield bomb from Scotland international halfback Peter Wallace found an unmarked Watene-Zelezniak, who touched down with eight minutes remaining to earn a handy 12-6 buffer.
The Raiders threw plenty at Penrith inside the final two minutes but the Panthers' defence held firm.
Idris then gave coach Ivan Cleary and the faithful Penrith supporters a huge scare when he offloaded a pass from an intercept break as the siren sounded.
The Raiders spread the ball before a kick found Penrith lock Adam Docker.
Meanwhile, Melbourne coach Craig Bellamy says suspended Storm prop Jordan McLean faces a "mental battle ahead" as he struggles with his role in the tackle that left Alex McKinnon with a serious spinal injury. McLean sat stone-faced throughout Wednesday night's judiciary hearing, in which he was given a seven-match NRL suspension after being found guilty of a dangerous throw.
In his first comments on the incident, Bellamy wrote in his column in The Weekend Australian yesterday of the Storm's plan to deal with McLean's welfare.
Bellamy also wrote of the Storm's desire to provide assistance to McKinnon and his family.
"Collectively, as a game, we are dealing with, and will continue to deal with the fallout of what in the opinion of many independent experts was an awful accident," Bellamy wrote. "We know that in sport inherent risk exists. Unfortunately, that doesn't mean it makes it easier to deal with injury when it occurs. Everyone at the Melbourne Storm wishes Alex McKinnon a full recovery.
"Their road ahead is going to be a difficult one and, as a club, Storm has expressed an ongoing desire to provide assistance.
"Likewise, everyone at the Storm is also gathering around young Jordan McLean, a respectful, humble young man, who has always had a genuine affection and care for his teammates and family.
"We've developed and implemented a plan that will hopefully help Jordan with the mental battle ahead.
"We see it as important that he stays in Melbourne, surrounded by teammates who've been outstanding at supporting him in a very private and respectful way.
"He has no family in Melbourne, so his teammates and our support staff at Storm are diligent in playing that role."
While the Storm remain undecided on whether to appeal McLean's suspension, they are trying to focus on tomorrow match with the Titans.
- AAP
