Southampton climbed above Manchester United into third place in the Premier League with a shock 1-0 win at Old Trafford, while Alexis Sanchez took centre-stage as Arsenal crushed Stoke 3-0 on Sunday.
Ronald Koeman's side stole the points in a dour encounter as Dusan Tadic's 69th minute strike boosted Southampton's bid to qualify for the Champions League via a top-four finish.
It was the Saints' first win over United since 2003 and their first at Old Trafford since 1988.
After a wobble in early December, Southampton are firmly back on track having beaten United and Arsenal, and drawn with Chelsea, in their last three league matches.
United, now two points behind Southampton, could have few complaints after a lacklustre performance which condemned them to their first home defeat since the opening weekend of the season against Swansea.
Louis van Gaal's team are without a win in their last three league games and recent talk of a potential title challenge is likely to be silenced as they lie 12 points behind leaders Chelsea.
Southampton have the best defensive away record in the top-flight and they easily frustrated United in a dull first half in which neither side managed a shot on target.
Koeman's side took the lead in the 69th minute when Graziano Pelle's shot hit a post and rebounded to Serbian midfielder Tadic, who swept his low shot past Tyler Blackett's attempt to clear off the line.
Juan Mata missed United's best chance, firing just wide, as the hosts pressed in vain for an equaliser.
- Majestic Sanchez -
At the Emirates Stadium, Sanchez delivered a majestic display as Arsenal kept up the pressure in the race for a top four finish with an emphatic win against Stoke.
Sanchez made Laurent Koscielny's opener and then netted his 17th and 18th goals of the season either side of half-time to lift Arsenal above Tottenham into fifth spot.
The battle for Champions League qualification is hotting up, with Arsene Wenger's side only one point behind fourth placed United.
"Collectively, you're happy when you score a few goals. We had a strong start and we knew that was vital today," Wenger said.
"Alexis Sanchez is one of the best players. He's a fighter with a combination of talent and fighting spirit which is very difficult to find.
"He plays with passion and you want people to enjoy what they're doing on the pitch and show it as well."
Just five weeks after Stoke's shock home victory over the Gunners, Arsenal legends Thierry Henry and Robert Pires watched from the stands as French defender Koscielny started the revenge mission with a sixth minute header from Sanchez's cross.
Arsenal right-back Mathieu Debuchy was forced off with a shoulder injury after tangling with Stoke's Marko Arnautovic.
"He has to see a specialist then we see where we go from there. A dislocated shoulder can take a while," Wenger added.
But the hosts struck again in the 33rd minute.
It was another moment of magic from Sanchez as the former Barcelona forward took Tomas Rosicky's pass and sized up his options before cleverly beating Asmir Begovic at his near post.
Sanchez wasn't finished yet and his deflected free-kick four minutes after the interval sealed the points.