Manly's loss was compounded by injuries to Daly Cherry-Evans (ankle) and Brenton Lawrence (pec) in the first half before losing Jamie Lyon to a leg injury shortly after the break.
Following a couple of error-riddled games in recent weeks, Canberra fullback Jack Wighton bounced back in the best way possible with a try, two assists and a pair of try-saving tackles to help his side knock off the Sea Eagles at home for the first time since 2004.
The early signs looked good for the visitors as Cherry-Evans took full advantage of back-to-back penalties to step his way through some over-aggressive inside defence to score inside five minutes.
The hosts should have hit straight back courtesy of a couple of quick penalties of their own, but Brenko Lee couldn't ground a Wighton grubber despite doing his best to sell it to the officials.
Thankfully for the Raiders it only took Lee two minutes to redeem himself; the former Junior Kangaroo finishing off a lovely right to left sweep to stroll over untouched in the left corner.
Wighton should have given his side the lead in the 28th minute but lost the ball over the line after some last-gasp intervention from State of Origin debutant Dylan Walker.
The Sea Eagles then nearly made it a 12-point turnaround through a hard-running Tom Trbojevic, but Wighton combined with the right-edge duo of Jordan Rapana and Joseph Leilua to bundle the Manly winger over the sideline.
The match looked destined to be level at the break, only for the Raiders to take some inspiration from the Maroons and score a crucial try in the shadows of half-time.
Heading into the contest as the game's leading offloader, Leilua added to his tally with a late pass to find Josh Hodgson before the English rake dummied inside on his way to the line. It was a perfect way for Hodgson to celebrate the birth of his child who entered the world on Thursday.
It took just four minutes for the hosts to extend their advantage after the break with another Leilua offload finding Josh Papalii who linked up with Elliott Whitehead; the Englishman stepping off both feet to cross for a brilliant team try.
The onslaught continued five minutes later as Wighton leapt highest to reel in an Aidan Sezer kick to score before the Raiders fullback put on a beautiful move close to the line to send Papalii over.
Matt Parcell darted from dummy half for what appeared to be a mere consolation try before Apisai Koroisau scored three minutes later from his own grubber to somehow set up a grandstand finish.
Manly looked set to make it three tries in five minutes when Trbojevic burst through the line but the Sea Eagles flyer was sensationally denied by Wighton to end any hopes of a miracle comeback.
Raiders 30 (Brenko Lee, Josh Hodgson, Elliott Whitehead, Jack Wighton, Josh Papalii tries; Jarrod Croker 5 goals) defeated Sea Eagles 18 (Daly Cherry-Evans, Matt Parcell, Apisai Koroisau tries; Dylan Walker 2, Jamie Lyon goals) at GIO Stadium. Half-time: 12-6 Raiders. Crowd: 9,157. Injuries: Cherry-Evans (ankle), Brenton Lawrence (pec), Jamie Lyon (leg).