Kilmarnock rallied from two goals down to win 3-2 at League Two Berwick, but League One Peterhead upset Dundee 2-1.
An Iain Vigurs hat-trick helped Inverness Caledonian Thistle to a comfortable 5-1 victory at Dunfermline.
Motherwell stuttered before beating East Stirlingshire 3-0, while Partick enjoyed a 4-1 win at Stenhousemuir.
Peterhead shocked Premiership side Dundee with a 2-1 win at Balmoor, leaving Paul Hartley's men with an uphill battle to progress.
Rory McAllister put the League One side in front just after the hour, and grabbed what proved to be the winner from the penalty spot with two minutes remaining.
Greg Stewart pulled one back for Dundee in the 90th minute, but it was not enough to save them from a damaging defeat.
Paul Hartley's side must now beat Forfar on Saturday and hope Dumbarton beat Peterhead to have even a slim chance of grabbing a best runners-up spot.
Forfar got the better of group leaders East Fife 2-0 at Station Park.
James Lister gave the League two hosts the lead before Andy Munro doubled it five minutes after the break.
The result keeps both teams still in the hunt. East Fife have finished their group games but could still be overtaken for a top-two finish on goal difference.
Brechin and St Johnstone could not be separated after 90 minutes, with the home side prevailing 4-2 in the penalty shootout to claim the bonus point.
Andy Jackson's bullet header gave the League One side a first-half lead, but Chris Kane rescued a draw for Saints with an equaliser four minutes from time.
Kane and Michael Coulson missed from the spot for Saints as Brechin secured two points to move within a point of their opponents at the top of the group.
Read the full match report here.
Stirling thumped League Two rivals Elgin 4-1 at Forthbank Stadium to leave them needing to take something at St Johnstone on Saturday.
Kyle MacLeod brought Elgin level after Edward Ferns' opener, but a second-half hat-trick from Blair Henderson sealed an emphatic win for the home side.
A hat-trick from Iain Vigurs helped Inverness thump Dunfermline 5-1 at East End Park and move joint-top of Group C.
Vigurs punished a poor kick from Pars keeper David Hutton to score from distance, against the run of play, and despite Andy Geggan's fourth of the season for the hosts, Vigurs' free-kick put them ahead at the break.
Billy King extended Caley Thistle's lead in the second half and Vigurs completed his hat-trick with a well-placed header.
Carl Tremarco's late fifth put the icing on the cake for a potent Caley side.
Arbroath and Cowdenbeath meet on Wednesday in the other Group C match.
Holders Ross County are out of the Scottish League Cup after falling to defeat at Alloa at a rain-sodden Indodrill stadium.
The home made the better of the conditions and led 2-0 inside 11 minutes with strikes from Jordan Kirkpatrick and Jon Robertson.
But the holders responded emphatically and drew level within 10 minutes as Alex Schalk powered in County's second after Brian Graham had reduced the arrears.
The visitors looked the more likely to find a winner but Calum Waters' strike 18 minutes from time saw County fall at the first hurdle.
Read the full match report here.
Cove Rangers host Montrose on Wednesday.
Partick Thistle edged a step closer to the last 16 with a comfortable 4-1 win at Stenhousemuir.
Mathias Pogba headed in from close range before Sean Welsh doubled their lead from the penalty spot.
Stenny gave themselves a fighting chance when Liam McCroary blasted home from the edge of the box to halve the deficit.
But David Amoo and Ade Azeeez fired in late strikes to preserve the Premiership side's 100% record at the top of Group E.
Queen's Park rallied from 3-1 down to rescue a point against Airdrieonians at Hampden, but lost the penalty shootout 8-7.
Adam Cummins put Queen's in front after just three minutes, but three goals in 12 minutes from Andy Ryan, Adam Brown and Iain Russell put the visitors in charge.
Aiden Malone reduced the arrears for the home side just after the break with Sean Burns equalising 11 minutes from the end, but it was Airdrie who claimed the bonus point with victory in the shootout.
Motherwell had to wait until the 53rd minute for a breakthrough against Lowland League East Stirling, beforeMarvin Johnson, Scott McDonald and Chris Cadden all struck in an ultimately comfortable 3-0 win which keeps alive their hopes of finishing second behind Rangers, who have already won the group.
Another victory at Stranraer on Saturday should see Mark McGhee's side progress as one of the best runners-up.
Read the full match report here.
Championship side Ayr made their superiority count with a 2-0 win at League One side Livingston.
Peter Murphy gave the visitors the lead on 19 minutes before Craig McGuffie completed the job 12 minutes from time.
Ayr top the table on nine points having completed their four games, but could still be overtaken by Hamilton, who visit Edinburgh City on Wednesday, and St Mirren.
Souleymane Coulibaly inspired a thrilling comeback as Kilmarnock avoided a cup shock against League Two outfit Berwick Rangers.
Goals from Jonny Fairbairn and on-loan Hibs youngster Sean Mackie had Lee Clark's charges staring down the barrel of a chastening defeat at Shielfield Park, following their home humbling by Morton.
But Coulibaly responded with two superb instinctive finishes in five minutes to restore parity, and the turnaround was complete after 85 minutes when Rory McKenzie headed home the winner to make it 3-2.
Killie are now likely to qualify if they beat Albion at home on Saturday, with leaders Morton hosting Berwick.
League Two side Clyde came from a goal down to register a victory at League One Albion.
Ross Davidson gave Albion the lead just before the hour mark, but Ewan McNeil and a 90th-minute Dylan Easton penalty gave Barry Ferguson's men their first win of the competition.
Just four months after they lifted the Scottish League Cup, Ross County are out of this season's competition after a 3-2 defeat at League One side Alloa.