Dortmund's 3-2 home loss to Bayern Munich last week all but ended their slim Bundesliga title hopes.

But Saturday's win took second-placed Dortmund eight points clear of fifth-placed RB Leipzig.

Beier teed up Guirassy in the 16th minute, floating a ball over the Cologne defence for the Guinean to score his 12th Bundesliga goal this season.

The hosts' hopes of fighting their way back dimmed just before half-time when Jahmai Simpson-Pusey planted his studs in Beier's heel and referee Daniel Siebert upgraded his yellow card to red after a VAR review.

Beier was in the thick of things again when he swept home on the hour mark. Jakub Kaminski scored a late consolation for the hosts but Dortmund held on for their first league victory since mid-February.

Dortmund manager Niko Kovac cut a frustrated figure after full-time, telling Sky Germany: "We won a game today in which we didn't play well -- and the coach has every right to be angry."

Kovac confirmed media reports midfielder Julian Brandt, who set up Beier's goal, would leave the club after seven seasons at the end of the season when his contract expires.

Bayer Leverkusen came from behind twice but gave up the lead late in a wild 3-3 draw at Freiburg, days out from their Champions League clash with Arsenal.

Leverkusen host the Premier League leaders on Wednesday in the first leg of their last-16 tie but Saturday's result left them in sixth and may hurt their chances of reaching next year's competition.

"We're more than a little disappointed," Leverkusen coach Robert Andrich told Sky Germany.

"Starting Sunday, we'll be focused on Arsenal, but we still need a lot of points in the Bundesliga to get back into the Champions League."

Freiburg twice went ahead thanks to goals from Vincenzo Grifo and Yuito Suzuki but Leverkusen twice equalised through Christian Kofane and another superb free-kick from Alejandro Grimaldo.

Martin Terrier's goal had the visitors on track for victory but Matthias Ginter struck with four minutes remaining to level things up.

- Leipzig leave it late -

Elsewhere, RB Leipzig forced Augsburg's Arthur Chaves into a stoppage-time own goal in a comeback 2-1 home win.

Robin Fellhauer gave Augsburg the lead after teammate Keven Schlotterbeck missed a penalty but Yan Diomande pulled one back for the hosts before Chaves scuffed a David Raum cross into his own net.

Leipzig's win took them to fifth, level on points with fourth-placed Stuttgart, who drew 2-2 at lowly Mainz.

Stuttgart fell behind to a Lee Jae-sung strike but looked to have turned the match with goals to Ermedin Demirovic and Deniz Undav inside 61 seconds, before Danny da Costa nabbed a late equaliser for the hosts.

"We fought hard for 90 minutes. When we fight back to take the lead, we need to take the three points," a disappointed Demirovic told Sky.

Hoffenheim took a step towards a second Champions League qualification with a 4-2 win at last-placed Heidenheim to stay in third.

Alexander Prass bagged a first-half brace and Fisnik Asllani and Tim Lemperle scored for the visitors, while Luca Kerber scored a double for Heidenheim.

Elsewhere, Hamburg came from a goal down to win 2-1 at Wolfsburg, with all three goals coming from the penalty spot.

Frustrated home fans threw flaming scarves onto the pitch after the defeat, which pushes second-last Wolfsburg, who were German champions in 2009, closer to a first relegation from the top flight since being promoted in 1997.