Stuttgart down Leipzig to strike blow in top-four race
Undav pounced on an error from Leipzig goalkeeper Maarten Vandevoordt to score his 16th goal of the season and move Stuttgart level with third-placed Hoffenheim on 50 points.
Bayer Leverkusen, who were held to a 1-1 draw by a nine-man Bayern Munich on Saturday, sit five points behind Stuttgart and two behind fifth-placed Leipzig in a tight race for next season's Champions League.
Stuttgart play at Porto in the Europa League on Thursday seeking to overturn a 2-1 first-leg deficit and reach the quarter-finals of the competition for the first time since reaching the 1989 final.
The best chance of the first half fell to Christoph Baumgartner, Leipzig's top scorer this season, but the Austrian blasted well over the bar when one-on-one with home goalie Alexander Nuebel.
With 56 minutes gone, Vandevoordt passed out directly to Stuttgart's Chris Fuehrich, who squared for Undav to slide home and score for a fifth straight game.
Leipzig's Willi Orban headed against the inside of the post in stoppage time but Stuttgart held on for a crucial victory.
Elsewhere, Jeong Woo-yeong scored in stoppage time and goalie Matheo Raab produced a spectacular late save on his Union Berlin debut as the visitors won 1-0 at Freiburg.
Union's first away win in 2026 took them seven points clear of the relegation playoff spot.
The teams had played scoreless draws in three of their past five matches and this game looked headed the same way until Woo-yeong curled a stunner through the crowded penalty box.
Raab leapt acrobatically to keep out a last-ditch Jan-Niklas Beste effort in the 12th minute of stoppage time.
Mainz won 2-0 at Werder Bremen to overtake the hosts and move three points clear of the relegation play-off spot.
A traditional giant in danger of a second relegation in six seasons, Bremen's woes were summed up when their defender Marco Gruell seemed to be distracted by a pigeon walking on the field as Mainz took a quick throw for Paul Nebel's fifth-minute opener.
Mainz's Lee Jae-Sung added another in the second-half to deepen Bremen's woes while boosting their own chances of survival.