Kieron Dyer earned Newcastle a place in the FA Cup quarter-finals as his goal proved enough to see off Southampton.
Newcastle match-winner Kieron Dyer gets in a first-half shot
Dyer struck after the break, rolling the ball into the bottom corner from Charles N'Zogbia's through pass.
The hosts wasted several first-half chances, Bartosz Bialkowski saving from Shola Ameobi, while Jean-Alain Boumsong and Ameobi also hit the woodwork.
Kenwyne Jones twice went close for Saints, while Peter Madsen clipped the top of the bar for the lively visitors.
Caretaker boss Glenn Roeder was forced to tinker with the Newcastle side with Alan Shearer injured, so Dyer made his first start since August.
He began brightly, finding space between Saints' back four and midfield and probing away to find an opening.
It was working, too, as first his pass found N'Zobgia, who crossed for Nolberto Solano to force a good save from Bialkowski.
Moments later Ameobi drilled a left-foot shot against the post from the left-hand edge of the area as the Magpies continued their early dominance.
Solano and Dyer were combining well and the former put Dyer through down the right, only for Bialkowski to make another impressive stop low to his right.
Saints only hope of scoring appeared to be the ineptitude of Jean-Alain Boumsong, and his terrible clearance almost led to Jones nodding in from 12 yards.
Just before the break, Newcastle twice thought they had done enough to go in front.
First Bialkowski produced a world-class save to tip over Ameobi's drive, before a Boumsong header bounced down and hit the angle of post and bar on the way up before Bialkowski caught the rebound.
Despite controlling long spells of possession, Newcastle's shaky back four always looked likely to make mistakes.
Robbie Elliott carelessly gave the ball away on the edge of the box to let in Jones, but his rasping drive cleared the crossbar.
Jones forced a brilliant save from Shay Given moments later before Alex Ostlund played Peter Madsen in, but his shot clipped the top of the bar.
The majority of the St James' Park crowd were becoming increasingly tense, but Dyer - who had drifted out of the game - calmed their nerves after 69 minutes.
N'Zogbia ran at the Saints defence from deep and slipped Dyer in, the 27-year-old keeping his composure to coolly slot past Bialkowski.
Bialkowski was forced off injured with 10 minutes left after landing awkwardly and as Saints had brought on three substitutes, Dexter Blackstock had to go in goal.
He managed to stop Newcastle increasing their advantage, but the hosts had done enough to progress to the last eight.
Newcastle goalscorer Kieron Dyer:
"The goal meant a lot to me, it felt so good just to be back out on the pitch.
"There was a lot of frustration coming out when I was celebrating the goal.
"All credit to Southampton, they played really well in the second half and we could have gone behind. But Charles N'Zogbia played me in and it went in."
Southampton head coach George Burley:
"Overall I'm disappointed not to get a draw and I felt we deserved it after how we had played.
"In the first half we defended for our lives, but after the break we were the better team and created four or five great chances without taking any.
"They were top-class chances too and you'll get punished against a team like this - you have to take one of them."
Newcastle: Given, Ramage, Bramble, Boumsong, Elliott, Solano, Parker, Emre, N'Zogbia, Dyer (Bowyer 76), Ameobi (Luque 70).
Subs Not Used: Harper, Faye, Clark.
Goals: Dyer 68.
Southampton: Bialkowski, Ostlund, Powell, Lundekvam (Potter 45), Brennan, Cranie, Wright, Jones (Blackstock 76), Oakley, Pahars (Dyer 45), Madsen.
Subs Not Used: Smith, Kenton.
Ref: M Atkinson (W Yorkshire).