On-loan Hearts midfielder Scott McGill hit a stunning debut goal as Airdrie shocked Motherwell 2-0 in the Lanarkshire derby at the Penny Cars Stadium.
Spectacular second-half goals from Rhys McCabe and McGill gave the Diamonds the bragging rights after the first meeting between the local rivals for 14 years.
The result leaves both sides on six points ahead of their final fixture with Group F leaders Queen's Park a point ahead but having played four matches.
Airdrie had some early aerial pressure but there was little other goalmouth action until Darragh O'Connor and Steven Lawless missed good headed chances either side of the break for Motherwell.
The hosts soon fashioned a chance following a long throw but Liam Kelly pulled off a brilliant stop from the unmarked Josh Kerr.
The match was livening up and Kaiyne Woolery forced a save from Airdrie goalkeeper Max Currie.
The hosts took the lead in the 66th minute when McCabe curled home a 30-yard free-kick and McGill arrowed a powerful strike into the top corner from 20 yards 11 minutes from time, just hours after joining the club.
Some home fans among the 2,000 crowd spilled onto the park after both goals while some of the 700 visiting supporters headed for the exits as soon as the second went in. They did not miss much of a fightback from their team.
Elsewhere, Dundee moved top of Group C thanks to a 2-0 win at Montrose.
Jason Cummings opened the scoring with a 70th-minute penalty and Luke McCowan netted on the rebound three minutes later.
James McPake's side moved a point in front of Forfar ahead of the visit of the Loons to Dens Park on Saturday.
Raith stayed top of Group D after holding Livingston to a goalless draw in West Lothian.
Dario Zanatta and Bruce Anderson threatened for each side before the latter was denied from point-blank range by Rovers keeper Jamie MacDonald.
Livi triumphed 6-5 on penalties to take what could be a crucial bonus point as they moved on to five points.
Falkirk's hopes of progress were ended by a Covid outbreak which forced a cancellation of their game against Edinburgh City.
City were awarded a 3-0 win which leaves leaders Ayr and Hamilton battling for top spot in Group E.
Ross County finally got their season up and running with a 1-0 win at Brora Rangers.
Alex Iacovitti's 53rd-minute header sealed the win but their hopes of progress had already been ended by a Covid outbreak which cost them six points.