A penalty with the last kick of the game earned Alfreton an undeserved point at the Martin and Co Arena.
Jonathan D’Laryea was the villain, bringing down Cecil Nyoni inside the box when he seemed to be going nowhere.
Dan Bradley dispatched the penalty despite the best efforts of Jan Budtz to put him off.
Trinity looked to be cruising towards victory until then, with centre half cum right back Jake Picton expertly volleying home to give the Blues the lead.
Trinity made one change to the side which drew with Stalybridge with Marc Newsham returning to the starting lineup in place of Craig Reid.
The change seemed to work in the first period with the Blues looking a lot more expansive going forward.
It was Newsham who had an early chance to put Trinity ahead when he met a Nathan Jarman cross with his head which drifted wide of the mark.
Jarman was the next to come close when a corner was not cleared, shooting across the face of goal and narrowly wide of the far post.
The former Alfreton striker then fizzed a free kick on goal which ex Bradford keeper Matt Duke palmed away and out of danger.
On the half hour, the visitors had their first chance. Todd Jordan leapt to meet a corner unmarked and did not really get anything on it when positioned around ten yards out.
Jarman then became the creator, fashioning two chances for teammates within minutes of each other.
First Simon Russell shot wide from the edge of the box after a lay off before a cute reverse pass freed Newsham in behind the defence and Duke saved the low drive with his feet.
Five minutes before the break Alfreton forced Jan Budtz into a double save. The Great Dane stopped a low Jamie McDonagh drive and then get back to his feet to prevent Tom Allan sidefooting home.
Trinity came out of the traps flying in the second half and began to dominate possession alongside territory.
Alfreton struggled to get to grips with particularly Jarman and Yates down the right hand side, where most of the Blues danger was coming from.
Jarman hit the roof of the net from 40 yards after spotting the keeper off his line before Yates picked out Picton in the box to head over the bar.
In the 64th minute, Picton got his goal though as two of the unlikeliest sources in the team, combined to full effect for Trinity.
Josh Lacey hit a long diagonal ball into the box which seemed to elude everyone, until the unmarked Picton appeared out of nowhere and expertly volleyed home.
It was the goal the game had been craving and it was what looked like the match winner for Gainsborough.
The only chance the visitors had in an attempt to get back in the game was a deflected header which had Budtz scared for a while, as Alfreton ran out of what little creative they had had in the first half.
Unfortunately, football is not game where the best team always wins and when Nyoni was brought down in the box, Bradley dispatched the penalty to equalise with the last kick of the game.
TRINITY: Budtz, Roma, Lacey, D’Laryea, Quinn, Picton, Yates, Russell, Newsham (Stamp 84), Jarman (Binns 90), Davis. Subs (not used): Rigby, Reid, Hedge.
ALFRETON: Duke, Allan, Banton, Jordan, Heaton, Nyoni, Doyle-Charles (Leesley 71), Wilson (Thanoj 23), McDonagh, Smith (Jackson 71), Bradley. Subs (not used): Meikle.
Goals: Picton 64 (Trinity); Bradley pen 90 (Alfreton).
Referee: Mr D Ford. Assistants: Mr C Hunter, Mr E Pidduck.