La Liga's top two meet in an eagerly anticipated match at the Vicente Calderon on Saturday as Atletico Madrid host champions Barcelona.
Gerardo Martino's Barca are top of the table on goal difference alone, and their opponents this weekend have displayed marginally better recent form in the league.
Atletico have taken maximum points from their last five games, keeping four clean sheets and seeing striker Diego Costa score six goals in the process.
Barca suffered their only league defeat of the season to date when losing 1-0 to Athletic Bilbao at the start of December, but have bounced back by taking nine points from nine since then and are boosted by Lionel Messi's return from a hamstring injury.
Messi scored twice after coming on as a second-half substitute in a 4-0 Copa del Rey win over Getafe on Wednesday, and will be looked upon to play a key role against Atletico.
Xavi, who was rested for the Getafe fixture, was delighted to see Messi back on the field ahead of a game he feels could prove crucial in deciding the destination of this year's title.
"It was an impressive return and (Messi) has clearly come back hungry and motivated," Xavi told Barcelona's official website.
"The game against Atletico is vital for the outcome of the league - it might not turn out to be definitive, but a win would lay down a marker."
In the last 20 years, Atletico and Barca have met as the sides ranked first and second in the table on only three occasions, with the men from Spain's capital winning two of those meetings.
Barca claimed the Supercopa de Espana when the teams last faced off, triumphing on away goals following a 0-0 draw in the second leg at Camp Nou.
Prior to the first leg of that tie in Madrid, which finished 1-1, the Catalan giants had won their last six games against Atletico.
In addition to welcoming back Messi, Barca are also expected to have Neymar available following a bout of gastroenteritis, while another forward, Pedro, is in fine form, scoring five goals in his last four appearances.
Atletico midfielder Koke has warned his team-mates not just to focus on FIFA Ballon d'Or candidate Messi.
"If he plays we have to be careful because he is the best in the world but Barcelona have great footballers and we must be aware of them all," said the midfielder, who scored the winner in Atletico's 1-0 victory at Malaga last weekend.
"It will be a very important game because the top two teams in the league play, (but) it is just another game and the whole second half of the season is to come.
"We know that to date it is the most important game."
Defender Diego Godin is a doubt for Atletico after picking up a thigh problem against Valencia in the Copa del Rey on Tuesday, while Mario Suarez (knee) is also likely to miss out.
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