The hosts were inspired by an outstanding display from Julian Ryerson, who was involved in all four goals. His pinpoint free-kick in the 10th minute set up Serhou Guirassy for the opener - Dortmund's league-high 10th Bundesliga opening goal from a set piece this season. Just five minutes later, Ryerson provided a second assist, with Maximilian Beier heading home to double the advantage.
Ryerson's delivery continued to cause havoc. His corner led to Guirassy's second goal shortly before half-time, taking the striker to 11 league goals for the campaign.
The Norwegian full-back then forced further chaos late on, as his ball into the area resulted in Dominik Kohr turning into his own net in the 84th minute. Ryerson was denied a fourth assist only by a sharp save from Daniel Batz.
Dortmund could have extended the margin further, with Batz producing key stops to deny Felix Nmecha, Beier and Julian Brandt, while Guirassy spurned a late chance to complete his hat-trick.
Mainz had opportunities of their own, as Silas dragged a side-footed effort wide and Silvan Widmer saw a goal ruled out for offside.
"We're happy, we're delighted with the win. It was hard-earned. The first half was evenly balanced, but we were more efficient. We steered the game in the right direction with our set pieces," said Dortmund coach Niko Kovac.
"We then controlled the second half. We had a few more chances, but a 4-0 win - especially without conceding - is very good.
"Everyone has a role to play in set pieces, and at the moment the lads are doing really well. When the balls come in like that, it's difficult for any team to defend.
"I'm delighted that all the hard work we've put in during set-piece training is paying off. We're keeping an eye on the rear-view mirror because the other teams are also playing well and having success."
The result keeps Dortmund unbeaten in 15 Bundesliga matches (11 wins, four draws) and the division's only side yet to lose at home. They trail Bayern Munich by three points, albeit having played a game more.
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