The visitors should have taken an early lead when a long ball forward caused problems for the home defence, but Franco Di Santo could only fire his shot over the crossbar from a promising position.
Despite being forced to work on the counter-attack for much of the game, the hosts came close to finding the opener when Marcel Risse's effort drifted just past the post.
A lapse in concentration gifted Werder the advantage as a corner drifted past a couple of defenders to reach Davie Selke, who finished calmly from close range.
The equaliser should have arrived before the break, but Anthony Ujah could only drag a shot past the post after being gifted space on the edge of the box.
Chances were difficult to come by for much of the second half, with Philipp Bargfrede left frustrated when his curling effort failed to come back enough to find the top corner.
It was the hosts who created the next opportunity after the hour mark as Yuya Osako lost his marker in the box before sending a header wide of the target.
Lehmann took on the responsibility from 12 yards and he finished emphatically to secure a draw for his side.