Saturday night turned out to be wonderful for world champions Barcelona, who are now five points clear atop the Spanish Liga, dpa reported.
Barca thrashed Sevilla 4-0 - with two more goals from FIFA World Player Lionel Messi - and second-placed Real Madrid surprisingly crashed 1-0 at Athletic Bilbao.
These results leave Barca with 46 points from 18 games, five points more than Real, and with the honorary title of "Winter Champions" because Real cannot catch them before the halfway stage, which is one weekend away.
"I am very happy tonight," said Messi, "because we played well and deserved this win."
He was quick to point out: "There is still more than half of the season to go, so we must continue to be as strong as we are now."
Barca were keen to take revenge on Sevilla for Wednesday's tight King's Cup elimination.
Sevilla came to the Camp Nou with a reserve-packed side and never looked capable of springing another surprise. They have slipped from third to sixth while losing their last four league games, their worst run since 2002.
Barca were imprecise in the first half but managed to translate their domination into goals after the interval. They went ahead five minutes into the second half when Sevilla defender Julien Escude clumsily turned a centre from Dani Alves into his own goal.
Supersub Pedro made it 2-0 20 minutes from time with a cool finish, after being put through by one of Xavi's majestic through- balls.
Pedro, the revelation of the Spanish season, has scored 14 goals in all competitions and might sneak into the Spanish World Cup squad.
Messi made it 3-0 eight minutes from time, after Alves put over yet another tempting centre. The little Argentine completed the rout in injury-time after being played through by Eric Abidal.
Messi is now atop the scorers' chart with 14 goals, two ahead of Valencia's David Villa.
Earlier Saturday, Real had surprisingly crashed 1-0 at Athletic Bilbao on an early goal from Spain striker Fernando Llorente.
"We worked really hard for this win," said Bilbao midfielder Markel Susaeta, "and the fans were just wonderful. They really helped us tonight."
The memorable win takes Bilbao - the only team in Europe's major leagues not to sign foreign players - up to seventh.
The Real players left the field astonished at losing a match in which they had enjoyed 62-per-cent possession and a plethora of clear goal chances.
Coach Manuel Pellegrini then raised eyebrows by saying: "There was only one team out on the field - Real Madrid."
Defender Raul Albiol said, "We deserved to score at least one goal. ... We should not really have lost tonight."
It was the first Real loss in old San Mames since 2004 and their third league defeat this season.
The Bilbao "Lions" made a fierce start, roared on by the most passionate fans in Spain.
In the second minute, first Carlos Gurpergui and then Gaiza Toquero hit Iker Casillas' posts. Then Llorente made it 1-0 by heading in a dangerous corner.
Real dominated from then on but lacked a cool finish with Gonzalo Higuain injured.
Karim Benzema hit the Bilbao post, and Cristiano Ronaldo and Kaka came close to equalizing three times each, only to be foiled by superlative goalkeeper Gorka Iraizoz.
Gurpegui was sent off in injury-time, as Real lay siege to the Bilbao goal.
San Mames then noisily celebrated the unlikely victory of an all- Basque squad of youngsters over the world's most expensive team.
The 18th round of matches had started earlier Saturday with Osasuna scoring a 2-0 home win over lowly Espanyol.
The hosts were two goals up within nine minutes, taking advantage of some sloppy defending from Espanyol.
Winger Juanfran gave Osasuna the lead in the seventh minute with a near-post shot, after a short corner from Javier Camunas.
And just two minutes later, old warhorse Walter Pandiani made it 2-0 by heading in a far-post centre from Camunas.
Osasuna had young midfielder Ruper sent off five minutes before half-time, but Espanyol defender Facundo Roncaglia followed him into the dressing rooms straight after the interval, making it 10 men per team.
Espanyol never looked capable of turning the match around in chilly Pamplona. They are now seventh from bottom, while Osasuna move up to 12th.