Nottingham Forest climbed out of the Premier League relegation zone and left Southampton rooted to the bottom of the table with a deserved 1-0 win at St Mary's.
After an impressive home draw with Chelsea on New Year's Day, 18th-placed Forest travelled to the south coast in search of their first away win this season and took the lead when Brennan Johnson, who had earlier rattled the crossbar from close range, pounced on a Lyanco error and raced clear before setting up Taiwo Awoniyi for a simple tap-in (27).
Southampton, who have now lost six consecutive league games, wasted an opportunity to take the lead in the first half when Che Adams fired wide but failed to register a shot on target and were again booed off by their own fans at the end of each half.
Southampton remain 20th after collecting just 12 points from 17 matches, while Forest rise to 15th having lost only two of their past eight.
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Jones: Saints' poor form not entirely my fault
Disgruntled Southampton supporters chanted 'you don't know what you're doing' at full-time as manager Nathan Jones' losing run since taking the job extends to four Premier League games.
"Whatever the fans think, we're in this situation. That isn't entirely my doing," he said.
"We've only won one game here in however many. I've only had two home games here and I've won one (against Lincoln in the Carabao Cup). I know the frustration, but it's not entirely my making.
"The players are low on confidence and the fans can get behind them, whatever they think. They want to see a result and a performance and we're trying to give them that.
"There's no lack of effort, maybe a little know-how and a little naivety, but when you're low on confidence things don't quite happen. But things will change and they have to get behind the team for that."
How Forest earned vital win
Nottingham Forest arrived on the south coast with the Premier League's worst away record, ready to take on the team with the poorest home form.
In a high-stakes encounter notable for Bhupinder Singh Gill becoming the first Sikh-Punjabi assistant referee to officiate in the Premier League, an elaborate light show illuminated the stadium ahead of kick-off and the energy initially transferred onto the pitch as both sides squandered glorious early chances.
Southampton's top scorer Adams was culpable first, skewing wastefully wide with time and space after being sent clean through by Kyle Walker-Peters following a poor clearance from Forest goalkeeper Dean Henderson.
The woeful miss was a major let-off for the visitors and they almost compounded Saints' frustration with their first attack.
After Awoniyi delivered a low cross from the left, Ryan Yates' mishit shot fell kindly to the unmarked Johnson but his rising effort struck the frame of the goal.
There was to be no second reprieve for Southampton as the slack defending which has been a hallmark of a dismal campaign once again led to their undoing. Saints defender Lyanco dithered and then sloppily conceded possession on halfway, allowing the jet-heeled Johnson to burst clear and square to Awoniyi, who tapped in to score his fifth goal of the campaign.
The breakthrough was only Forest's second goal on the road in the league this season and broke a six-game drought dating back to a 1-1 draw at Everton in August.
Saints conjured nothing in response before the break and suffered the recurring ignominy of being jeered from the field by their success-starved supporters.
The home side enjoyed plenty of possession during a tight second period but failed to test Henderson, while appearing susceptible to counter-attacks.
They were given four minutes of added time to chase a valuable leveller. However, Forest were more than comfortable and jubilantly celebrated a first top-flight away win since a 2-1 success at Blackburn in May 1999.
Steve Cooper's resurgent side have now taken 11 points from the last 21 available, having only managed six from the previous 33.
Jones: Saints have a mountain to climb
Southampton manager Nathan Jones said: "It does [give us a mountain to climb]. We started the game really well, on the front foot and had a glorious opportunity to take the lead and didn't take it and we gifted them a goal. We know if you play square or loose balls into midfield, you are susceptible to giving the ball away.
"We never demonstrated enough quality in possession. We had enough possession around the box, but we didn't convert that into chances. That's the frustrating thing. We needed to be braver and bolder with our passing at times, and we weren't. That allowed Forest to sit in and we couldn't break them down.
"It could have been different, but we have to do certain things better for the scoreline to change. One, we need to keep clean sheets. Two, we need to take chances. Three, we need to show more bravery in the final third. Once we do that, we give ourselves the chance to win the game."
Cooper: Forest fans overdue an away win
Nottingham Forest head coach Steve Cooper said: "When the game settled, we were by far the better team and the first half we controlled.
"I challenged the players not to shy away from the fact that we've not picked up enough points away from home. And we're going to have to start doing that. We wanted to face up to that and didn't think about Southampton and league positions.
"All of our fans deserve credit for this year but it was great for the away fans. I know away tickets are hard to get so I know there are regular away travellers who haven't seen us win away in the league. So they deserved that tonight.
"It's a reference point for sure. It [getting out of the bottom three] is something we've wanted to do. It's easier said than done, we know how hard these games are. We've just got to continue and take it step by step, with the culture and togetherness."
Is there any way back for Southampton?
Sky Sports' Dan Sansom:
It may have seemed slightly strange to suggest before kick-off that Southampton needed the win more than Nottingham Forest considering both sides started the evening in the relegation zone, but Nathan Jones' team were in desperate need of three points as they looked to lift themselves off the foot of the Premier League table.
Against a Forest team that had only scored once on the road this season and were yet to win away from home, it was, at least on paper, an ideal opportunity for Saints to breathe some much-needed life into their survival bid.
But it never looked like happening. They failed to register a shot on target as they deservedly fell to a sixth consecutive league defeat. Six points from a possible 27 at St Mary's this term says it all.
The club's decision to sack Ralph Hasenhuttl in November and appoint former Luton boss Jones is yet to be vindicated. 'You don't know what you're doing', disgruntled home supporters chanted at the final whistle. It's four league defeats out of four for the Welshman. He has had a brutal start to life as a Premier League manager.
Unless the Southampton board backs him with some quality signings in the January transfer window, it's likely to get worse. At the moment, his side look destined for Championship football next season, a division he knows all too well.
Forest buoyed by Johnson's return to form
Sky Sports' Sam Johnston:
Nottingham Forest's first away win of the season provided further evidence that Brennan Johnson is in the process of rediscovering his best form. The 21-year-old started the season brightly with two goals in Forest's six games of the season but then failed to find the net - or an assist - before going to the World Cup with Wales, and even found himself dropped to the bench on a couple of occasions.
However, a little bit of time to recover after Wales' group-stage exit appears to have worked wonders for Johnson, who has appeared re-energised since domestic football resumed. He scored twice at Blackburn as Forest eased into the Carabao Cup quarter-finals in their first, and was a constant threat as Steve Cooper's side outplayed Chelsea at the weekend.
Against Southampton on Wednesday he made a decisive contribution, seizing on Lyanco's error to race clear and calmly set up a tap in for Taiwo Awoniyi. His performance was backed up by the numbers too, with Johnson leading Forest in chances created (3), dribbles completed (3) and tackles made (2).
"Brennan very rarely makes the wrong decisions, he always makes the right decision for the team," Cooper said. "Tonight he made the right decision. And they deserved the goal and the assist."
With the win having elevated Forest out of the bottom three, there is little doubt Johnson's performances will need to remain at a high level if they are to remain clear of the drop zone.
Fantasy Premier League stats
Opta stats: Jones' poor start continues
- Nathan Jones is just the second manager to lose each of his first four Premier League games in charge of Southampton, after Nigel Adkins in the 2012/13 season.
- Southampton failed to have a single shot on target in a Premier League game for the second time this season (also vs Man City in October) - no side has failed to do so in more matches this term.
- All four of Nottingham Forest's Premier League wins so far this season have been 1-0, with Taiwo Awoniyi netting the winner in three of those.
- All four of Taiwo Awoniyi's Premier League goals this season have been the opening goal of the game. Only Erling Haaland and Harry Kane (5 each) have scored first in more different Premier League games this season.
What's next?
Southampton travel to Crystal Palace in the FA Cup third round on Saturday (kick-off 12.30pm) before hosting Manchester City in a Carabao Cup quarter-final on January 11 (kick-off 8pm), live on Sky Sports.
Up next for Nottingham Forest is a trip to Blackpool in the third round of the FA Cup on Saturday (kick-off 3pm). Forest then play Wolves at home in the last eight of the Carabao Cup next Wednesday (kick-off 7.45pm).
Both sides return to Premier League action on January 14 as Southampton travel to Everton (kick-off 3pm) and Nottingham Forest host Leicester (kick-off 3pm).