Mainz piled the pressure on local rivals Eintracht Frankfurt with a last-gasp 1-0 win at the Coface Arena.
Eric-Maxim Choupo-Moting scored in the 88th minute of the Rhine-Main derby, earning Thomas Tuchel's men only their second win in their past nine Bundesliga games and extending Frankfurt's winless run to seven.
The victory lifts Mainz up to eighth ahead of Stuttgart's clash with Freiburg while Frankfurt could drop into the bottom three should Freiburg win that derby on Sunday evening.
Frankfurt forward Alexander Meier said before the game that he had learnt over the years how big a derby this fixture had become, and he nearly gave the visiting fans some joy in the fourth minute when he rose to head the ball against the angle of post and crossbar.
Another high ball into the area almost set up Vaclav Kadlec, but he was unable to bring the ball under control as another chance went begging for the visitors.
Mainz's first threat arrived midway through the first half when Shinji Okazaki found a way through, but Kevin Trapp held his nerve to deny him in a one-on-one situation.
A distance effort from Zdenek Pospech was next to test Trapp, who responded at full stretch to tip the ball over.
Both sides continued to attack in an entertaining game which nearly opened up within seconds of the restart when Sebastian Polter was denied by the increasingly busy Trapp.
Mainz started to gain the upper hand, but Trapp was always there to deny them. He blocked another Polter effort before watching an Elkin Soto effort go wide.
When it seemed like he had done enough to earn the Eagles a point, he was finally beaten.
Pospechs lofted cross to the far post was met by a determined Choupo-Moting, who headed the ball down into the bottom left-hand corner with Trapp this time beaten, and the points were Mainz's.