Jan Rosenthal scored twice, but later became one of five players sent off in Saturday's six games, as Freiburg came from behind to extend Schalke's winless run to six league games.
The only consolation for their fiery coach, Huub Stevens, was sports director Horst Heldt's promise on Thursday that the Dutchman's job is safe for the time being.
Kiessling's brace made the unsung striker the Bundesliga top scorer with 12 goals. Andre Schurrle was also on target as second-placed Leverkusen cut Bayern Munich's lead at the top to nine points at the Bundesliga's halfway mark.
Bayern slipped up on Friday when they were held 1-1 at home by Borussia Monchengladbach, only the fourth time this season they have failed to win.
Promoted Eintracht Frankfurt went third with a 2-0 win after some early drama at VfL Wolfsburg. Alexander Meier and Takashi Inui scored for Eintracht while Wolfsburg had Josue sent off for a studs-up challenge, all in a six-minute spell before the 20th minute.
Greuther Fuerth and Augsburg both finished with 10 men as they drew 1-1 in a meeting of the bottom two, leaving them level on nine points from 17 games at the foot of the 18-team table.
Sascha Molders gave Augsburg an early lead and Lasse Solbiech levelled after the break for Fuerth, who are in the Bundesliga for the first time and have yet to win at home.
Fuerth's Mergim Mavraj was dismissed for a second bookable offence, and his sending off was followed by that of Augsburg substitute Giovanni Sio, who got a straight red after only four minutes on the field.
Two goals from Nicolai Muller helped Mainz 05 to a 3-1 win over VfB Stuttgart and promoted Fortuna Dusseldorf beat Hannover 96 2-1.
LEADING SCORER
Kiessling has been among the Bundesliga's leading scorers over the past few seasons but has won only six caps for Germany, finding himself overshadowed by Miroslav Klose and Mario Gomez.
Leverkusen reached the halfway mark with 33 points, compared to Bayern's 42, with Frankfurt a further three points behind.
Leverkusen's progress has gone almost unnoticed with Bayern hogging the limelight, and Schurrle said they did not expect to mount a challenge, despite the Bavarians' recent tendency to cave in at crucial moments of a campaign.
"Bayern are simply too good this year, we have to accept that," Schurrle told reporters.
"But we want to cut their lead as much as possible and, naturally, we won't want to give up on second place."
Leverkusen went ahead when Kiessling side-footed past Rene Adler from an unmarked position in the 26th minute after Gonzalo Castro deflected the ball into his path.
Ten minutes later, Kiessling threaded a ball into the area for Schurrle, who burst past his marker and shot past an exasperated Adler, who was again exposed by his defenders.
Adler was angrier at Leverkusen's final goal, in the 66th minute. L
