Compounding the Raiders' home loss, inspirational co-captain Simaima Taufa appeared to injure her right shoulder attempting a tackle in the second half at GIO Stadium on Saturday.
She managed to play through the pain despite reeling out of the contact in significant pain, clutching the same shoulder she hurt during the grand final of the NSWRL Women's Premiership in May.
Canberra cannot afford to lose middle forward Taufa as they fight to overcome an inferior points differential and lock up a finals berth in their inaugural season.
Sitting atop the ladder temporarily, Newcastle would need to be handily beaten in their remaining two games and have a host of other results go against them to fall out of the top four from here.
The reigning premiers trailed 10-0 at halftime after Raiders winger Madison Bartlett bagged a pair of tries on the left and the Knights' halves failed to boot them into the ascension.
But when Newcastle fullback Tamika Upton, arguably the form player in the league, began to take the contest on in the second half, the script flipped dramatically.
Five-eighth Georgia Roche spun out of the goal-line defence before Southwell had a hand in the two tries that confirmed all momentum for the visitors.
The teenage star first looped a cut-out pass to Sheridan Gallagher on the right wing and then levelled the scores with a pinpoint sideline conversion.
Only three minutes later, Southwell dummied right and then stepped inside past Petesa Lio for a try of her own.
Newcastle's win sets up a compelling heavyweight clash with the Sydney Roosters next week.
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