* Messi scores twice in 5-1 home victory
* Barca set record for best La Liga start
* Atletico beaten 2-0 at Real in Madrid derby
* Valencia sack coach after defeat by Sociedad (Adds Real-Atletico result)
By Iain Rogers
MADRID, Dec 1 (Reuters) - Unbeaten leaders Barcelona pulled six points clear of chasing Atletico Madrid and set a record for the best start to a La Liga season when Lionel Messi scored twice in a 5-1 drubbing of Athletic Bilbao on Saturday.
After an imperious Barca had crushed the struggling Basques at the Nou Camp, goals from Real Madrid's Cristiano Ronaldo and Mesut Ozil dashed Atletico's hopes of a first win against their city rivals in more than a decade.
Jose Mourinho's side, in third place after a poor start to their title defence, turned in a dominant performance at the Bernabeu to put last week's defeat at Real Betis firmly behind them and their 2-0 victory trimmed the gap to Atletico to five points.
Fourth-placed Malaga slumped to a 1-0 defeat at Getafe, while 10-man Valencia's 5-2 drubbing at home to Real Sociedad left them mired in 12th place and prompted the club to sack coach Mauricio Pellegrino.
With 14 matches played, Barca lead on 40 points, with Atletico second on 34 and Real on 29, seven ahead of Malaga.
"We obviously needed to beat them as they are a direct rival for the title and it was a good performance tonight," Real midfielder Xabi Alonso said in an interview with Spanish broadcaster Canal Plus.
"We controlled the match very effectively and we need to continue in the same vein," added the Spain international.
The 164th league meeting between Barca and Bilbao was another stroll for Tito Vilanova's men, who were 3-0 ahead by halftime at the Nou Camp thanks to goals from Gerard Pique, Messi and Adriano.
Cesc Fabregas and Messi added two goals after the break, either side of an Ibai Gomez effort for Bilbao, with Argentine World Player of the Year Messi taking his tally for the season in La Liga to 21 in 14 matches, eight ahead of Ronaldo.
The 25-year-old is now only one short of the record haul for club and country in a calendar year of 85 set by former Germany and Bayern Munich striker Gerd Mueller in 1972.
Barca's record of 13 wins and a draw improves on the previous best start to La Liga of 13 wins and a defeat by Real in the 1961-62 campaign.
"We enjoyed it a lot and we got the best out of everyone," Fabregas told Spanish broadcaster Canal Plus.
"It was extremely challenging physically but it was worth the effort," added the former Arsenal captain.
With Atletico resurgent under Argentine coach Diego Simeone, hopes were high they could secure a rare win against Real, who were under pressure after the defeat in Seville left them 11 points behind bitter rivals Barca.
Portugal forward Ronaldo ended a rare scoring drought in the 16th minute when his blistering freekick was too good for Thibaut Courtois in the Atletico goal.
The visitors barely troubled Real keeper and captain Iker Casillas and Ronaldo, who twice struck shots against the frame of the goal in the second half, played in Germany playmaker Ozil to double the home side's lead in the 66th minute.
It was an impressive response from the Real players after some fans vented their frustration by whistling Mourinho during a King's Cup match on Tuesday.
The victory extended their La Liga unbeaten streak against their city rivals to 22 matches, a run stretching back to Oct. 30, 1999.
At Getafe's Coliseum stadium, Albert Lopo headed home from a corner in the 56th minute and Malaga missed several good chances in the latter stages before Getafe midfielder Diego Castro was sent off for a second yellow card in added time.
"We lost a match in which Getafe had one attempt on goal in 90 minutes," Malaga coach Manuel Pellegrini, whose side are through to the last 16 of the Champions League on their debut in the competition, told a news conference.
"They were able to score the goal that won them the match from a corner," added the Chilean. "We had three clear chances and we didn't take them."
Getafe's victory lifted them to sixth, level on 22 points with Malaga and fifth-placed Real Betis, who play at Deportivo La Coruna on Sunday.
Spain striker Roberto Soldado opened the scoring for Valencia in the second minute at the Mestalla before forward Jonas was shown a straight red card for an elbow on David Zurutuza in the 41st minute.
The Brazilian's senseless dismissal allowed Sociedad to take charge and defender Alberto de la Bella levelled three minutes later before Mikel Gonzalez made it 2-1 to the Basque side 11 minutes after the break.
Diego Ifran sped clear to add a third in the 64th, Soldado grabbed his second of the night nine minutes later, substitute Imanol Agirretxe made it 4-2 seven minutes from time, and Carlos Vela rounded off the victory from the spot in added time.
It was the ninth goal Valencia had conceded in their last two La Liga outings after a 4-0 thrashing at Malaga last week and the fans voiced their displeasure at the end with grim-faced club president Manuel Llorente watching from the stands.
Llorente later announced he had sacked Pellegrino, who took over from Unai Emery at the end of last season although they do not have an immediate replacement.
Valencia, who are through to the Champions League knockout round, are mired in 12th place on 18 points, while Sociedad climbed to seventh on 20, level with eighth-placed Levante who visit promoted Celta Vigo on Sunday. (Editing by Greg Stutchbury)