Nigerian Obasi, replacing the injured Jefferson Farfan on the right wing, made the most of a rare start this season to lift Schalke to 54 points, two ahead of Borussia Dortmund who travel to relegation-threatened VfB Stuttgart on Saturday.
Schalke, who have lost once - against Bayern Munich - in their last 13 league games as they chase a Champions League qualifying place, went in front after 16 minutes when Obasi shook off two markers and rounded the keeper to score.
Schalke, who also hit the woodwork in the first half, looked livelier despite injuries to 10 players.
Netherlands striker Huntelaar notched his 11th goal in 13 league matches this term seconds after the restart by drilling in a low shot having been sent through by Nigeria forward Obasi.
Hertha remain in ninth place after their fourth straight league defeat.
Bayern, who secured the title on Tuesday with seven games left in the campaign, host mid-table Hoffenheim on Saturday.
- Sports & Recreation
- Borussia Dortmund
- Bayern Munich
- VfB Stuttgart