Atletico Madrid host Barcelona at the Wanda Metropolitano on Saturday, knowing that a win could see them leapfrog Ernesto Valverde's side to go top of La Liga.
It will be a game of contrasting styles, with Atletico's tight, defensive approach going up against a lethal but vulnerable Barcelona. Will Atletico's defence stand up to the test or will Barcelona's forwards run riot?
Here are three key battles to keep an eye on.
3. Jan Oblak vs. Marc-Andre ter Stegen
Two of the world's best goalkeepers go face to face on Saturday. In a game that is likely to be decided by fine margins, both men could have a big part to play in the final result.
Ter Stegen made a terrible mistake last time out against Betis, for which he will be looking to make amends. Oblak very rarely makes mistakes but he doesn't come up against Luis Suarez and Lionel Messi every week, so he can't afford to be complacent.
Oblak is currently on course for a fourth consecutive Zamora trophy as Atletico have the tightest defence in the division at present, while Barcelona's defensive record is that of a bottom half side. Advantage Atletico?
2. Antoine Griezmann vs. Gerard Pique
Two excellent players who haven't hit their best form yet this season. Antoine Griezmann only has three La Liga goals to his name, while Gerard Pique has played every minute of league action for a Barcelona side which hasn't kept a clean sheet since August. Something has to give on Saturday.
Extra spice is added to this battle by Griezmann's decision to reject Barcelona and sign a new contract with Atletico during the summer. He'll be determined to prove that he made the right decision; Pique will be equally keen to prove him wrong.
1. Lionel Messi vs. Lucas Hernandez
This match could be one of the biggest tests of Lucas Hernandez's Atletico Madrid career so far. An injury crisis has struck Diego Simeone's defence with Diego Godin, Jose Gimenez and Stefan Savic all doubtful for this weekend's match, potentially leaving 22-year-old Hernandez as the only senior centre back available for selection.
Youngster Francisco Montero made his first La Liga start against Athletic Bilbao before the international break but Barcelona is a different prospect entirely. Hernandez must give Montero the confidence to keep the league's most prolific attack at bay.
That won't be easy when Lionel Messi is in this sort of form, with 14 goals in 13 appearances so far this season, including a brace last time out against Betis. He loves playing against Atletico, with 28 goals in 32 appearances versus Los Rojiblancos. It's up to Hernandez to make sure Messi doesn't add to that tally.