The Sea Eagles have continued their giant-killing finals run in the Holden Cup with an upset 34-18 win over the Dragons to book a spot in the NYC grand final thanks to a stunning solo display by halfback Cade Cust.
Having finished the regular season in eighth spot, Manly have claimed wins over the fifth-placed Cowboys, the minor premiers, Cronulla, and the Dragons, who earned a week off after a narrow victory in the qualifying final.
Next week will be Manly's first appearance in the decider since 2015, while they are the first eighth-placed side to reach the grand final since the Warriors carved up the competition in 2014.
St George Illawarra might have started slowly but they had all the running for the middle 40 minutes as they dominated possession and territory, however they were left to rue several blown chances as they fell to their sixth loss from as many preliminary finals.
Missed opportunities dictated the opening 15 minutes of the contest with Jackson Ford and Brayden Gallagher spurning great chances for the Dragons while the Sea Eagles were unable to find the line despite five sets in in a row in the red zone.
The weight of possession finally told when lock forward Haumole Olakau'atu bashed his way through to give Manly the lead and it didn't take them long to double their advantage when rampaging centre Tevita Funa burst into the clear and put in a spectacular banana kick to find Jade Anderson back on the inside to make it 12-0.
Things were looking dicey for the Red V until Trent Peoples steadied the ship with a powerful run one off the ruck to cut the gap to six points after 30 minutes.
The comeback was short-lived, however, as Olakau'atu strolled over for his second courtesy of a magical no-look inside pass from Cust to make it 18-6 at the break.
St George Illawarra enjoyed a perfect start to the second half when a game of pinball near their line ended up in the hands of big man TJ Uele who unloaded the ball to Joe Lovodua who stepped his way through to reduce the deficit.
Momentum was all with the Dragons who went agonisingly close on several occasions before they finally drew level when Jackson Willis pretended to kick, sliced through and then grubbered ahead for Ford to score an amazing team try.
The Dragons had a chance to take the lead when they were awarded a penalty from the next set within range, but Willis hooked his shot to leave the scored locked at 18-all with 14 minutes remaining.
Having defended their line for what seemed like 20 minutes straight, Manly finally worked their way into good field position and made the most of their rare opportunity when Cust delivered another stunning flick pass to Olakau'atu who showed enough strength to crash over for his third try of the afternoon.
A six-point lead was never going to be safe, and having laid on a number of four-pointers for his teammates, Cust sealed his side's passage to the grand final with a couple of solo tries at the death to cap an outstanding individual performance.
Sea Eagles 34 (Haumole Olakau'atu 3, Cade Cust 2, Jade Anderson, tries; Tevita Funa 5 goals) def. Dragons 18 (Trent Peoples, Joe Lovodua, Jackson Ford tries; Jackson Willis 2, Reuben Garrick 1 goals) at Allianz Stadium. Half-time: Sea Eagles 18-6.