Newcastle defender Federico Fernandez scored a late winner as his side came from behind to beat Southampton at St James' Park.
Fernandez fired in a rebound from close range after Sean Longstaff's shot was parried by keeper Alex McCarthy.
His 87th-minute winner came after Jonjo Shelvey had cancelled out Danny Ings' opener with a second-half header.
Newcastle have not lost at home in the Premier League since the opening weekend.
- Reaction to Sunday's Premier League
Ings, scoring in his fifth successive match for Southampton, latched on to a long ball which Newcastle had failed to clear and slotted it past Martin Dubravka.
That came after a bright spell for Newcastle at the start of the second half but the hosts were dragged back into the match by Shelvey - now the team's top scorer in the Premier League with five goals - who was set up by a curling cross from substitute Andy Carroll.
Southampton responded and should have regained the lead through Ryan Bertrand, who missed a header from a few yards out at the back post before Ings came close to connecting with Shane Long's low cross.
Nathan Redmond also missed chances for Southampton in the first half - he fired straight at Dubravka after picking up a loose pass and was denied again by the keeper when he struck powerfully inside the box.
Defeat leaves Southampton in the relegation zone - level on points with Aston Villa - while Newcastle break into the top 10.
Shelvey stars again as Magpies keep climbing
Before the match Newcastle boss Steve Bruce described their run of fixtures in December - which, including Southampton, contained three teams in the bottom half of the table - as "season defining."
They began the month with a 2-0 win at Sheffield United and go into next Saturday's game at Burnley on the back of successive victories, scoring twice in each game.
Crystal Palace come to St James' Park after that, before two potentially tricky fixtures against a revived Manchester United and Everton but Newcastle will be brimming with confidence after this energised run of results.
Things have slotted into place since Shelvey's late equaliser against Manchester City and the midfielder was to thank again for his side's turnaround in this match.
He keeps delivering big goals when it matters and Bruce will be boosted by Carroll's cameo from the bench which included an assist.
Allan Saint-Maximin must be given huge credit too - he was the best player in the first half and remains a constant threat for Newcastle on the wing.
Missed chances costly for Saints
It was a heavy blow for Southampton, who drop back into the relegation zone despite creating numerous chances away from home.
They should have lead at half-time when Redmond failed to put away his opportunities and when the ball came to Bertrand late on in the second half, he did not react quick enough to direct his header.
Chances came and went for Ings and Long but they were punished for their lack of clinical edge.
Ings, who has now scored eight of Southampton's last 13 goals in the Premier League, was lively throughout but his side cannot rely on him alone to deliver goals.
And since Ralph Hasenhuttl's first game in charge exactly a year ago, Southampton have lost five league games in which they have opened the scoring - more than any other side.
'Big Andy was a huge help' - what they said
Newcastle boss Steve Bruce, speaking to Match of the Day: "In the first half we looked like we had played three games in six days. I felt we were flat and it was not really until we changed things at half time and went higher up the pitch we caused them some problems. They stuck at it, they showed a bit of spirit.
"The introduction of 'Big Andy' [Carroll] had glimpses today of what he had 10 years ago. He looks well at the moment. Big Andy Carroll coming on was a huge help."
Southampton boss Ralph Hasenhuttl, speaking to Match of the Day: "I thought [defeat] was not deserved. It was our best away performance of the season. We had chances to be more than 1-0 up. It was a pity. Really frustrated for the guys.
"After we scored, I think we stopped a little bit playing. They had a big guy in front and only went for long balls. The first goal we didn't defend well and the second was a shot from outside the box. It is a pity, I didn't see a lot of chances for Newcastle today, plenty for us. We didn't get the result but it was a very good game from us."
Man of the match - Allan Saint-Maximin
Surpassing expectations - the best of the stats
- Newcastle are unbeaten in seven Premier League games at St James' Park - they never surpassed this number under Rafael Benitez, last having a longer such run in April 2012 under Alan Pardew (nine games).
- They have also earned 22 points from their opening 16 games this season, nine more than they had at the same stage last season.
- Ings is the third player to score in five consecutive Premier League games for Southampton, after James Beattie and Matt Le Tissier, who both did so twice.
- Southampton's last 13 Premier League goals have been scored by Englishmen.
- Shelvey has netted six goals in his last 12 appearances - his previous six Premier League goals were spread across 116 matches.
- Saint-Maximin attempted 18 dribbles against Southampton, the last Newcastle player to attempt as many in a Premier League game was Hatem Ben Arfa in December 2013 against Stoke City (also 18).
