The Black Cats fifth draw on the trot leaves them 13th of the Premier League on nine points, leveling with Blackburn.
Egypt wing-back Elmohamady made his eighth start of the season for the visitors, who struggled in vain to beat the resilient Paul Robinson at Ewood Park.
Elmohamady picked up his first caution of the season following a foul on French defender Gael Givet just before the break.
A few minutes later, Rovers were a man down when Christopher Samba was given a straight red card for shoving the clear-on-goal Danny Welbeck.
But Sunderland, who only scored seven goals in eight games so far, couldn't find the net through some shy attempts from marksman Darren Bent.
The Black Cats host Aston Villa at the weekend before clashing with bitter rivals Newcastle in the often-tense Tyne-Wear derby by the end of the month.