Vedad Ibisevic struck twice as Hoffenheim regained their spot atop the Bundesliga with victory at Cologne.
Demba Ba gave the league newcomers the lead after 32 minutes before both teams saw a man get sent off early in the second half.
Kevin McKenna was red carded after 52 minutes for the hosts before Hoffenheim saw Luiz Gustavo given his marching orders four minutes later for a second bookable offense.
The league's leading scorer Ibisevic made it 2-0 after 67 minutes before Petit pulled a goal back in the 78th. But Ibisevic struck again with two minutes left for his 16th goal of the season.
The victory for Ralf Rangnick's team was their seventh in the past eight games and gives them 31 points - three points ahead of Bayer Leverkusen, who lost today at Arminia Bielefeld, and Bayern Munich.
Cologne dropped their second straight game after two consecutive wins to remain on 19 points and in 10th place.
Hoffenheim had the first real chance as Matthias Jaissle got to Sejad Salihovic's free kick after five minutes but sent the header over the crossbar from five yards.
Cologne keeper Faryd Mondragon did a fine job stopping Salihovic's 30-yard blast in the 19th minute.
Christoph Daum's Cologne were stronger but missed a series of chances.
And once again, Hoffenheim punished their opponents for not scoring, taking the lead after 32 minutes. Carlos Eduardo passed into Ibisevic, who one-timed the ball to Ba and the Senegalese beat Mondragon to the left corner off the post and in.
McKenna was sent off seven minutes after the break for his tackle on Salihovic.
But Hoffenheim's player advantage was lost just four minutes later when Luiz Gustavo was shown his second warning.
Hoffenheim beat an offside trap on a long ball in the 67th minute but Salihovic was stopped by Mondragon only to have the ball land directly at the feet of Ibisevic, who slotted home.
Marvin Compper saved a goal by stopping Geromel's header two minutes later, but Cologne pulled a goal back with 12 minutes left as Ba deflected Petit's free-kick from 20 yards out to leave Haas with no chance to save.
But Ibisevic made sure of Hoffenheim's win with two minutes left with a long run from his own half before beating Mondragon from the right wing.
