Heart of Midlothian are through to the last 16 with a game to spare after beating Stirling Albion 2-0 at Forthbank while Cove Rangers defeated Inverness CT 3-1 at Balmoral Stadium.
Dundee United booked their place in the knock-out stages with a 1-0 win at East Fife while Kelty Hearts were 3-1 winners away to Elgin City.
Both matchday four games are on Wednesday, with Brora Rangers at home to Ross County and Montrose taking on Dundee at Links Park.
Brechin City beat Alloa Athletic 1-0 at Glebe Park while Livingston host Raith Rovers on Wednesday.
Ayr United are top of the section after a 1-0 victory at Hamilton Accies while Edinburgh City take on Falkirk at Ainslie Park on Wednesday.
Queen's Park defeated Annan Athletic 2-1 at Galabank. Airdrieonians host Motherwell on Wednesday, live on Premier Sports.
Kilmarnock and Morton drew 1-1 at Rugby Park, with Killie winning the penalty shoot-out. East Kilbride and Clyde drew 2-2 at K-Park, with the visitors picking up the bonus point.
St Mirren lead the way with maximum points after a 3-1 victory over Stenhousemuir at Ochilview and Partick Thistle beat Dumbarton 2-0 at Firhill.