By Iain Rogers
MADRID, Jan 30 (Reuters) - Real Madrid's 11-match unbeaten run has lifted confidence and closed the gap on La Liga leaders Barcelona and Atletico Madrid but their form faces a stern test at Athletic Bilbao's new San Mames stadium on Sunday.
The Basque club, fiercely proud of their heritage and always keen to thwart their detested rivals from the capital, are fourth, largely thanks to their record at home where they have won 11 and drawn two in front of their passionate supporters.
They are the only team who have beaten champions Barca, a 1-0 success at the San Mames at the beginning of December, and Real's task may be made even harder as Bilbao will still be smarting after being dumped out of the King's Cup by Atletico on Wednesday.
Carlo Ancelotti's Real side have not been tested since they needed a late winner to secure a 3-2 victory at Valencia at the end of December but another victory on Sunday (2000 GMT) would be a big fillip as they head towards a key stage of the season in La Liga, the King's Cup and the Champions League.
Defeat could see them fall four points behind in the title race and burst the bubble of optimism that has grown around the club in recent weeks.
"It's very important," Ancelotti told a news conference on Tuesday after Real's 1-0 win at home to Espanyol secured their place in the Cup semi-finals.
"It's a tricky match because Athletic are playing very well at the moment and everyone knows playing at the San Mames is not easy," added the Italian, in his first season in charge since taking over from Jose Mourinho.
"But it's a good time for us to be playing there. We have confidence and desire and we are excited about giving everything to win."
Ancelotti may be without record signing Gareth Bale for the trip north.
The Wales winger, whose first season in Spain has been disrupted by minor injuries, had to come off at halftime in last weekend's 2-0 win at home to Granada due to a problem with his left leg and missed the Cup game against Espanyol.
Ancelotti said if Bale was unavailable, forward Jese would likely be deployed up front alongside regulars Cristiano Ronaldo, the FIFA Ballon d'Or winner and La Liga top scorer with 22 goals, and Karim Benzema.
Barca and Atletico, who top the table on 54 points from 21 matches, with Real a point back at third, also have potentially tricky games this weekend, with Barca hosting mid-table Valencia on Saturday (1500) and Atletico at home to sixth-placed Real Sociedad on Sunday (1800).
The joint leaders returned to winning ways last weekend after consecutive draws, including a 0-0 stalemate between the pair at Atletico's Calderon stadium.
Valencia were the last team apart from Barca and Real to win La Liga, back in 2004, but their financial struggles have seen them morph into one of Spain's also-rans who can barely manage to qualify for European competition.
Barca playmaker Andres Iniesta is not taking the game lightly, however, even though Barca have won their last 25 league games at the Nou Camp, stretching back almost to the beginning of last season.
"We know that playing Valencia here is always tough," the Spain international told reporters after Wednesday's King's Cup quarter-final success against Levante.
"Although it might be different from other years, we have to take the match seriously and really go for the win," he added.
"The team is in good shape, in a very good moment in every sense. The hardest part of the season is still to come but it's also the most enjoyable." (Editing by Sudipto Ganguly)