The Power found a way to hold off the plucky Saints, who responded well from an embarrassing 60-point defeat to the Western Bulldogs last week.
After leading by 13 points at the final break, Port battled on to win 11.16 (82) to 10.12 (72) at the Adelaide Oval on Friday night.
The Power were forced to play out the final quarter with just two fit players on the bench after losing Rozee (hamstring) and Powell-Pepper (knee) during the third quarter.
Zak Butters was his usual force for Port, racking up 27 possessions. (Matt Turner/AAP PHOTOS)
Aliir was subbed out for Jackson Mead after being concussed in the second term following a tackle by St Kilda forward Jack Higgins, who will face a nervous wait before the match review officer delivers his findings.
The trio will almost certainly be ruled out of the Power's Showdown with Adelaide back at the same venue on Thursday night.
Powell-Pepper was only playing his third game since a four-match suspension for a high bump during a pre-season hitout and there are genuine fears he could have suffered a ruptured anterior cruciate ligament.
Veteran key forward Charlie Dixon stepped up with four goals while his Power teammates struggled for accuracy.
In his 100th game, star midfielder Zak Butters was Port's leading possession-winner with 27, while Willie Rioli stepped up with two goals from his limited opportunities.
"It was a fitting day for our club, playing (a day after) Anzac Day and finding courage to get over the line," Port coach Ken Hinkley said.
"Initially, it was hurting ourselves with conversion, and then it became about us running into concrete walls a bit and hurting ourselves physically so pretty proud of the boys to get that job done."
St Kilda's Jack Sinclair tries to escape Esava Ratugolea en route to a match-high 28 disposals. (Matt Turner/AAP PHOTOS)
St Kilda suffered an injury scare of their own, with ruckman Rowan Marshall forced off early in the match with a suspected knee injury.
But Marshall was able to return and play out the game as St Kilda tried to combat the star-studded Power midfield and a lopsided free-kick count, 25-10 in Port's favour.
St Kilda coach Ross Lyon said he doesn't buy into umpiring and even asked what way the free-kick count went.
"Oh did it? Nah. That's not what cost us the game," Lyon said.
"Umpires do a bloody hard job. If I'm sitting here talking about rub of greens and umpires consistently then I'm in the wrong chair."
Jack Sinclair, Nasiah Wanganeen-Milera and Brad Hill were St Kilda's best in their third-straight defeat.
Inaccurate Port moved to 5-2 this season with their 13th win from their last 14 meetings with St Kilda.
The result consigned the Saints to a 2-5 record ahead of a clash with lowly North Melbourne next Saturday.
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