Sunderland climbed out of the Premier League relegation zone after holding Arsenal to a 0-0 draw at the Stadium of Light.
Sam Allardyce’s men have moved above Norwich City into 17th place on goal difference after a spirited performance against the Gunners in which they created the better chances to win.
Defoe, left isolated for much of the half, saw his frustrations increase as he fired Hector Bellerin’s poor clearance straight into Mertesacker’s raised arm, only for referee Mike Dean to wave away his appeals for a penalty.
And Iwobi was aggrieved not to earn a spot-kick for Arsenal just before the break after his shot struck the arm of the sliding Yedlin following Olivier Giroud’s superb lay-off.
Sunderland held firm for a deserved draw that gives them real hope of beating the drop. The Gunners, meanwhile, must continue to look nervously over their shoulder towards Manchester United in fifth.