Mo Dahoud, Jadon Sancho and Reinier scored the goals after the interval for the Black & Yellows, who ran out 3-0 winners after a goalless first half at Signal Iduna Park.
The victory means its now three wins in a row across all competitions for Edin Terzic’s side ahead of a busy week – with a game against Monchengladbach in the DFB Pokal before the Klassiker next weekend against Bayern Munich.
Dortmund had some good news ahead of kick off, with Roman Burki, Dan-Axel Zagadou, Thorgan Hazard and Lukasz Piszczek all returning to the squad after lengthy spells out and taking their places on the bench. There were two changes from the derby win over Schalke a week earlier, with Jude Bellingham replacing the unwell Thomas Delaney and Gio Reyna replacing Julian Brandt.
It was the hosts who created two good chances early on. Emre Can played a ball in behind and Marco Reus cut it back to Bellingham, whose shot was blocked by Cedric Brunner and Amos Pieper in the six yard box, with Raphael Guerreiro firing the follow-up wide.
Reyna then went close with a shot that fizzed past the post barely a minute later, but Arminia had two early chances of their own. Ritzu Doan’s effort from just outside the area just missed the target, before Marwin Hitz made a good save to keep out Fabian Kunze after twelve minutes.
But for all Dortmund’s possession, they were kept at bay by their well organised opponents, until Terzic’s men upped the tempo after 25 minutes. Sancho’s free kick was spilled by Stefan Ortega and although Mats Hummels’ follow-up was blocked, Reus had a clear sight of goal but only to be denied by the crossbar.
Guerreiro then cut in to find Erling Haaland, who in turn found Reus, only to be denied by Ortega before Sancho won the ball back and was quick to find Haaland inside the area – but the Bielefeld keeper stuck out an arm to save.
The opening goal was coming – but in the end it almost came at the other end just before half time, however Sergio Cordova could only rush his shot from a promising area and fired wide of the goal.
And the breakthrough duly came for the hosts just three minutes into the second period. Dahoud initiated the goal himself when he picked the ball up after an attempted clearance and found Sancho on the left. The Englishman cut inside and teed up Dahoud, whose low shot from the edge of the box found the bottom corner – it was Sancho’s 50th assist in 99 games, with no other player having reached that landmark in fewer than 100 matches.
The Bielefeld rear-guard could not get a grip on the young Englishman and he picked out Reus, who was felled by Pieper in the box. Had referee Reichel hesitated for a spilt second before pointing to the spot, Reyna had put the ball in the net, but in the end it didn’t matter as Sancho stepped up to send a low shot past Ortega and into the bottom right corner from the spot.
Dortmund had dropped off a bit after going two goals ahead, but Reiner – who had only been substituted on 28 seconds earlier – put the game to bed with ten minutes to go. Haaland was the architect, who after playing a one-two with Reus broke through on goal before teeing up the youngster.
Bielefeld was the first of five matches in the space of 15 days for Dortmund, who if they maintain this form could yet break into the top four of the Bundesliga table despite it looking unlikely a few weeks ago.