Both men bagged a double, with Simmons taking his try tally for the season to 19.
The result ended a four-match losing streak for Penrith, who move level with the Warriors on 22 points, two points outside the top eight with three rounds to go.
But the defeat in Auckland was a big disappointment for the home side, who held an early 12-0 lead and have now lost three in a row.
They threatened their own comeback midway through the second half when bench prop Suaia Matagi produced a typical charging run from 20 metres out to dot down for a converted try that closed the margin to 22-18.
But Sika Manu's reply after a big break by former Warriors player Isaac John restored Penrith's 10-point margin.
The Warriors did manage to set up a grandstand finish for the 11,596 fans when centre Konrad Hurrell scored with eight minutes to go and Shaun Johnson converted from wide out.
But that was as close as they got and Simmons almost had the last say, but was held-up in his attempt to complete a try hat-trick.
For the Warriors, the loss was compounded by injury to centre Dane Nielsen, who limped off early in the opening spell after a tackle on opposite Dean Whare.
Before he went off, the Warriors had jumped out to 12-0 lead with tries to Thomas Leuluai and Penrith-bound Elijah Taylor.
Leuluai's touchdown was created by Nathan Friend's deft kick into the in-goal, while a Johnson pass put Taylor into a big hole.
But the Panthers picked up their game and dominated the rest of the half, forcing the Warriors into plenty of defence.
With prop Tim Grant leading the way up the middle, they caused problems with their width on attack and profited with tries to their wingers.
Mansour forced his way over for the first, although John's final pass looked forward.
Simmons then produced a superb one-handed diving put-down in the other corner for the second.
Three minutes from half-time, Simmons got his second, and the second of Luke Walsh's sideline conversion pushed Penrith out to a 16-12 advantage.
The Panthers went further ahead midway through the second spell when Mansour pounced to a Lachlan Coote kick just inches inside the in-goal.
PENRITH 28 (J Mansour 2 D Simmons 2 S Manu tries L Walsh 4 goals) bt WARRIORS 24 (K Hurrell T Leuluai S Matagi E Taylor tries S Johnson 4 goals) at Mt Smart Stadium.
Referees: Jason Robinson, Chris James.