Borussia Dortmund blew the Bundesliga title race wide open with a 4-1 win over Hertha Berlin on Sunday, but in-form striker Karim Adeyemi limped off clutching his hamstring in the first half.

The win saw Dortmund pull level on points with league leaders Bayern Munich and high-flying Union Berlin, who were held to a 0-0 draw at home to Schalke earlier on Sunday.

"We're on a great run of form and we want to keep riding this wave and see where it leads in the end," said captain Marco Reus.

Adeyemi's injury made for a bittersweet evening, with the 21-year-old limping off almost in tears just minutes after putting his side on their way with a quickfire goal and assist.

Dortmund started a little sluggishly after their 1-0 Champions League win over Chelsea in midweek, and Hertha could have taken the lead when Jessic Ngankam skimmed the bar early on.

The Signal-Iduna-Park was soon bouncing, though, as Adeyemi gave Dortmund the lead with a brilliant backheel on 27 minutes.

Adeyemi set up Donyell Malen for his side's second with a brilliant cross four minutes later, but was already clutching his hamstring as he curled the ball into the box.

After the match, Dortmund manager Edin Terzic said Adeyemi "would probably miss a few games" but asked for "a little time" so the club could get an official diagnosis.

There was fresh hope for relegation-threatened Hertha when Lucas Tousart thundered the ball in off the bar just after the break to halve Dortmund's lead.

But Dortmund overcame their nerves once more and Reus smashed a direct free-kick into the top corner to restore the two-goal cushion.

Julian Brandt made it four late on, linking up with Jamie Bynoe-Gittens to score for a third league game in a row.

In one of the most intriguing Bundesliga title races for years, Dortmund, Union and Bayern are now all on 43 points after Bayern's surprise defeat to Borussia Moenchengladbach on Saturday.

"There's a long way to go yet, not just for us, but also for Union and Bayern," said Brandt.

In Sunday's late game, a late penalty from Danish forward Marcus Ingvartsen helped Mainz record a valuable 3-2 victory away at Bayer Leverkusen.

In a fiery encounter, which saw 10 yellow cards, Amine Adli was shown straight red for bringing down Silvan Widmer in the box after 81 minutes, with Ingvartsen stepping up to break the deadlock.

The win saw Mainz leapfrog Leverkusen into ninth place, inflicting a third loss in four games on the home side.

Union missed the opportunity to leapfrog Bayern into first with a miserable 0-0 draw at home to bottom club Schalke.

Schalke have now battled to a league record four goalless draws in a row, and they frustrated Union with another dogged performance.

In a torturous first half for spectators, the only moment of relief came when Schalke keeper Ralf Faehrmann pulled off a brilliant reflex save to deny Danilho Doekhi.

Schalke looked the more dangerous side in the second half, with Union appearing to be running on empty after their Europa League draw with Ajax last Thursday.

US international Jordan Pefok missed a chance to snatch a late winner when he skied a tough chance high over the bar from close range on 81 minutes.

"It's normal that we have the odd game like this and Schalke played really well. We know every point is important and I am happy that we are still unbeaten this year," said Union captain Christopher Trimmel.

Union remain in the title race ahead of their clash with reigning champions in Munich next weekend.

Schalke, meanwhile, are still six points adrift of safety, having not won in the league since last November.