The Tunisia international received a long throw from goalkeeper Christian Wetklo on the halfway line, flicked the ball into space and then beat onrushing custodian Raphael Schafer to make it 3-0.
In Saturday's other games, eighth-placed defending champions Bayern Munich host Eintracht Frankfurt, third-placed Bayer Leverkusen travel to fellow Champions League hopefuls Hoffenheim and fourth-placed Hannover are at home to Freiburg in another top-end clash.
Schalke will seek to continue the club's recent revival and leapfrog 13th-placed hosts Kaiserslautern, while fellow strugglers Stuttgart are at home to mid-table Hamburg.
On Sunday, Wolfsburg travel to second-bottom Cologne and out-of-form Werder Bremen host St. Pauli.
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