Jens Keller's side were always in command at the Veltins Arena, and wasted several opportunities to add gloss to the scoreline against a below-par Frankfurt side.
But it mattered not as Schalke cruised to a deserved victory to move level on points with second-placed Borussia Dortmund ahead of their local rivals' daunting trip to champions Bayern Munich on Saturday.
Despite dictating much of the game, it took Schalke until the 59th minute to open the scoring, which they did through attacking midfielder Max Meyer.
The 18-year-old slotted into the net on the second rebound after Klaas-Jan Huntelaaer's shot had been brilliantly saved by Frankfurt goalkeeper Kevin Trapp following Sead Kolasinac's fierce long-range effort, which rattled off the post.
Schalke then thought they had doubled their lead when Julian Draxler's tame effort squirmed under the body of Trapp, only for the strike to be chalked off for offside.
The hosts were handed another opportunity to extend the lead in the 64th minute as they were awarded a penalty following Carlos Zambrano's foul on Draxler.
However, Huntelaar saw his spot-kick saved by Trapp to keep Frankfurt in the contest.
Leon Goretzka hit the post nine minutes from time as Frankfurt's goal continued to lead a charmed life, but the result was finally made safe in the first minute of injury time, as substitute Jefferson Farfan found the net with a superb curling free-kick.
