Lionel Messi's 45th Clasico on Saturday could also be his last as Barcelona look to rubberstamp their progress under Ronald Koeman by beating Real Madrid and claiming top spot in La Liga.
The reward for the winners at Valdebebas will be knocking Atletico Madrid out of first place for the first time since December, before they mounted a run that saw them go 10 points clear with a game in hand at the start of February.
But Atletico's recent struggles, combined with a surge in momentum for Madrid and Barca, has seen that advantage evaporate, the question now whether Diego Simeone's team can recover and regroup to even stay in the race through the final stretch.
Who Atletico have to hold off or, more likely, catch in the last nine games could depend on this weekend's result at the Alfredo di Stefano stadium, where both clubs will be hoping for the ultimate vindication of recent improvement.
Success for Barcelona would be another significant check-point too in what has been an uplifting few months, the start of a recovery that has run alongside the ongoing uncertainty of what Messi will decide this summer.
Messi's every goal and glance this season has been analysed for possible indications as to the 33-year-old's thinking but what is clear is how the atmosphere at Barca has changed since he asked to leave for free last August.
Joan Laporta's election as club president, replacing Josep Maria Bartomeu, has brought enthusiasm and, crucially, a sense of direction again, even if the financial problems from the last regime are still very much the problems of the new one.
Messi is not expected to consider offers to renew his contract until the end of the season but Laporta has been pulling hard on the heart-strings.
"Today was the 20th anniversary of a boy named Leo Messi who debuted in the youth teams of Barca," Laporta said in his victory speech last month.
"To see Leo come to vote, the best player in world soccer, with his son for me, is an example of what we've said, that Leo loves Barca and how we are all one big family."
