Rooney's missed spot kick costs Latics
Adam Rooney missed a penalty in time added on to deny Latics a share of the spoils after Sam Manton had given the Saddlers the lead just after the hour mark.
The second half opened at a similar pace the way the first half ended, both sides zipping the ball around the wet surface. Danny Philliskirk raced onto a Michael Petrasso through ball only to be blatantly pulled back, again referee Graham waving away Latics appeals.
The Saddlers earned the first corner of the half after Genserix Kusunga had blocked an attack down the left, Oxley making a superb full length save to deny Paul Downing from Westcarr's kick .
A superb free kick from Dayton, after Korey Smith had been upended as he raced towards the box, struck the upright with keeper O'Donnell stranded, Philliskirk was first to the loose ball but his snap shot was inches wide of opening the scoring.
On 62 minutes Grounds became the first player to enter referee Graham's book after his rash challenge left Sam Manton on the floor.
GOAL 1-0 Manton exacted his revenge just a minute later as he swept a loose ball into the corner of the net after the Latics defence had failed to clear a ball in from the right.
Johnson replaced Petrasso and MacDonald with Jonson Clarke-Harris and Harkins before play restarted.
Oxley kept his side in the game on 70 minutes diving to his left to keep out a decent effort from Romaine Sawyers as the home side looked to put the game beyond Latics.
O'Donnell made a superb save on 77 minutes to deny Harkins his first goal for the club, the on loan striker's free kick destined for the bottom corner until the big keeper leapt to keep it out.
Adam Rooney replaced Philliskirk on 80 minutes as manager Johnson looked to give his side another attacking option.
Rooney missed a glorious opportunity to level the scores on 87 minutes, slicing his effort wide after superb build-up play between Harkins and Dayton, the latter's cross finding Rooney free at the far post.
In added time Rooney missed the best chance of a late leveller as his penalty was saved by O'Donnell, the spot kick was awarded after James Wesolowski had been brought down in the box. Rooney's kick was struck well enough but O'Donnell dived to his right to make the save of the night and seal the win for his side.
FT: Walsall 1 Latics 0
ATT: 3,522 (182 )
Latics: Oxley, Grounds, Wesolowski, Kusunga, Tarkowski, Smith, Mellor, MacDonald (Harkins), Petrasso (Clarke-Harris), Dayton, Philliskirk (Rooney).
Unused Subs: Rachubka, Rodgers, Lockwood, Brown.