Scott Gallacher starts in goal for St Mirren this afternoon as Jack Ross makes two changes from the side that lost 1-0 to Dumbarton last weekend.
Out go Jamie Langfield and cup-tied Ben Gordon to be replaced by Gallacher and Jack Baird.
Youngsters Kyle Magennis and Kyle McAllister keep their place in the starting XI after impressing last week with the latter picking up man of the match.
Kick-off against Ayr United is at 12:30pm as the Saints look to join Dundee United and Queen of the South in the semi-finals of the IRN-BRU Cup.
St Mirren XI: Gallacher, Naismith, Baird, MacKenzie, Irvine, Mallan, Magennis, McAllister, Clarkson, Morgan, Sutton
St Mirren Subs: Langfield, Stewart, Hutton, Walsh, McLear, Gallagher, Shankland
