Hannover have not lost at home in the Bundesliga for nearly 18 months and ex-Manchester United striker Diouf preserved their proud record at the AWD-Arena with an 86th-minute equaliser as the hosts finished with a flurry.
With Bayern Munich five points clear at the top of the table after their 2-0 win over Hoffenheim on Saturday gave them a Bundesliga record-equalling seventh straight victory, Dortmund are now nine points behind the Bavarians.
Their point also came at a price as midfielder Jakub Blaszczykowski came off after 39 minutes with a leg injury, while defender Mats Hummels aggravated his hip problem and midfielder Ilkey Gundogan missed the game with a back strain.
"We have three injured players in the dressing room and conceded a late equaliser," said Dortmund coach Jurgen Klopp.
"We should have finished our chances. We will play our own season. We have two games against Bayern Munich. These games interest us greatly, but not the (points) deficit after only seven matches."
Dortmund took an early lead that was made in Poland as defender Lukasz Piszczek found some space in the Hannover penalty area and squared to his Polish team-mate Robert Lewandowski, who fired home on 26 minutes.
Hannover had their chances to equalise, with Ivory Coast striker Didier Ya Konan then second-half replacement Diouf only being denied by good work from the solid Dortmund defence.
The equaliser finally arrived when Ya Konan fired in a shot that Diouf managed to latch onto before stabbing the ball past despairing Dortmund goalkeeper Roman Weidenfeller.
Bayer Leverkusen finish the weekend sixth in the table after a 2-2 draw at Stuttgart, with ex-Germany striker Stefan Kiessling scoring twice for the guests while Vedad Ibisevic netted both goals for Hoffenheim.
Earlier, second-place Eintracht Frankfurt suffered their first league defeat of the season after going down to a shock 2-0 loss at Borussia Mönchengladbach.
Having won promotion from the second division in May, Armin Veh-coached Frankfurt had previously won six of their seven games since coming up, while this was only Gladbach's second league win of the season.
The victory moved Gladbach up to 10th in the table, while Frankfurt stayed second after goals by Venezuela veteran Juan Arango and Dutch striker Luuk de Jong put the hosts 2-0 up after only 24 minutes.
On Saturday, there was no happy return to Gelsenkirchen for Wolfsburg's ex-Schalke coach Felix Magath as the Royal Blues enjoyed a 3-0 win.
Magath spent two years at Schalke before he was sacked in February 2011, when he returned to Wolfsburg.
Magath's team were well beaten at Veltins Arena thanks to goals by Peru striker Jefferson Farfan, Dutch forward Ibrahim Afellay, and midfielder Roman Neustädter.
It was Wolves' sixth game without a win and their third straight defeat, leaving Magath's team second from bottom, while Schalke moved up to third.
Hamburg continued their rise up the table to eighth with a 1-0 win at Bavarian side Greuther Fuerth thanks to South Korean striker Son Heung-Min's first-half goal.
Mainz enjoyed a 1-0 win at home to Fortuna Düsseldorf, while Freiburg recorded their first win in four games with a 3-0 victory at home to Nuremberg.
On Friday, Werder Bremen lost 3-1 at Augsburg as the hosts enjoyed their first win of the season.