For the second game in succession, Nick Blackman netted but the latest of late goals earned Oldham a point.
Blackman confidently slotted home a second half penalty after Dave Kitson was fouled by Jean Yves M'voto but substitute Matt Smith scored in the seventh of three injury-time minutes.
It was United's fourth consecutive home draw at the Lane.
Chief Wilson was forced into two changes for the home encounter with Oldham Athletic. With Howard injured, Long took over in goal, whilst with Gallagher's loan not being extended, Cofie was recalled. Academy prospect Chapell was on the bench and joined by 17-year-old youth team goalkeeper, Willis.
Cofie took up a place on the left flank and got involved with a number of the early touches but the first opportunity of the game was from Kitson flicking on Long's big clearance - Blackman laid off to Flynn but McDonald, arriving in the box unmarked, could not find the target.
A heavy and persistent shower made conditions difficult but Hill kept his footing to cut out a Derbyshire cross and Doyle was well placed to block from Wabara. However, on 20 minutes, the Blades almost contributed to Oldham taking the lead. A number of attempted clearances had gone astray before McDonald gave away possession and the subsequent break saw Simpson's shot parried by Long - Grounds slotted home the loose ball, but he was denied by a flagging referee's assistant.
With the Blades struggling for rhythm, Derbyshire headed wide from a Baxter free-kick and McDonald picked up the game's first yellow card, on 35 minutes, for a late connection with Montano, who was also the recipient of a challenge from McMahon just before the break when the United defender was also booked, despite Oldham's players surrounding the referee.
The start of the second half began with a long run and cross from Williams, who caused a nervy moment for goalkeeper Bouzanis, who, moments later, turned a half-volley from Doyle around the post after good work from Cofie. The lead, however, was just moments away.
Hill's up and under saw Kitson and M'voto challenge before the visiting defender put his hands on the Blades striker and pulled him back - right in view of referee Mathieson, who immediately pointed to the spot. BLACKMAN took responsibility and ignored the poor attempt at gamesmanship from goalkeeper Bouzanis to slot home in front of the Kop.
Montano fired over and Derbyshire's flicked header was wide as Oldham attempted to respond, whilst on 65 minutes Long made a tremendous save to protect the lead, palming away a shot from Derbyshire after a flick on by Croft. Blackman and M'voto both picked up for bookings for exchanging words and United's first change was Cresswell replacing Cofie.
Hill was booked for his protests after Long was smashed into by Simpson and as the game entered the final 15 minutes another flicked Derbyshire header was wide. With five minutes remaining Flynn had the chance to double the lead but after intercepting a pass from Wabara and cutting inside M'voto, he sidefooted wide.
M'voto was added to the Oldham attack late on and goalkeeper Bouzanis went forward for a corner but Long saved from Smith's header before three additional minutes were signalled. United were content to keep hold of possession and there was a delay when M'voto and Hill clashed heads but more drama was to follow...just like Oldham's last visit to the Lane.
A hoopeful ball into the box from the left resulted in SMITH surprised to see himself in space and he slotted under Long from just six yards. There was just time to restart before referee Mathieson brought an end to proceedings.
Blades: Long, Maguire, Hill, Flynn, Doyle, Blackman, McDonald, Kitson, Cofie (Cresswell 70), McMahon, Williams.
Unused: Westlake, Porter, Miller, McAllister, Chapell, Willis.
Oldham: Bouzanis, Grounds, Wesolowski, Yves M'voto, Croft, Derbyshire, Simpson (Smith 82), Montano, Byrne, Baxter, Wabara.
Unused: Cisak, Brown, Tarkowski, M'changama, Winchester, Sutherland.