Bielefeld, who had not won in seven games, moved out of the automatic relegation places to 15th and gave new coach Frank Kramer his first win after three matches in charge. Mainz are now second-bottom with Hertha Berlin in the relegation play-off spot.

Doan slid in to give the visitors the lead off the underside of the bar on 18 minutes. Leverkusen dominated possession and produced some half chances before Okugawa struck his first Bundesliga goal on the break in the second half.

Patrik Schick netted for Leverkusen on 85 minutes and Lucas Alario went close to a late leveller but otherwise Bielefeld confidently saw out the win.

Sixth-placed Leverkusen, top in December, could have gone fourth temporarily with a win but their wildly inconsistent season took another strange turn.

Eintracht Frankfurt stay fourth and visit second-placed RB Leipzig later Sunday before VfB Stuttgart face fellow midtable side Hoffenheim in the final game of the day and weekend.