Marc McNulty's last gasp penalty sends the Sky Blues to Meadow Lane level with their play-off rivals after an action packed 1-1 draw at the Ricoh.
Jonathan Forte gave County the lead just after the break with a delightful flick that beat Lee Burge from close range.
City ended the game by throwing everything at their opponents and were rewarded in the final minutes when Tom Bayliss was fouled in the area, allowing McNulty to confidently step up and fire City level.
Mark Robins' side head to Meadow Lane on Friday for the second leg.
The Sky Blues started the stronger in the Ricoh rain. Jordan Shipley played an exceptional ball over the top for McNulty to chase into the area before the 25-year-old let fire across the 'keeper and off the far post. Biamou did he best to chase it down but his rebound was well blocked by Richard Duffy. The Ricoh was rocking.
The visitors were not without their chances, however. Jonathan Forte scored the winner when the two sides met last month and almost had the game's opener after 15 minutes. The former Southampton man jumped highest in the area to make first contact with a County corner but headed over the bar.
County came close again moments later. Their best chance to hurt the Sky Blues was from a set piece and forced some impressive acrobatics from Lee Burge once again after Forte's header forced the City 'keeper to hook the ball off the line with his feet. The atmosphere was beginning to hot up.
The EFL's goal line decision system was in use for the first time at the Ricoh Arena and was needed shortly before half time. McNulty found himself again bursting into the area to cross low for Biamou who battled with County 'keeper Collin on the goal line forcing the referee to look at his watch before waving play to continue.
The best opportunity of the first half fell to teenager Tom Bayliss. The 19-year-old made the most of a lapse in concentration at the back to find himself face to face with Collin, only to drag his effort skimming wide through the puddles.
Sadly for the Sky Blues, County were ahead almost immediately after the break. Some nice play down the left saw the shipped to Daniel Jones on the touchline, who beat Grimmer and crossed low for Forte to flick under Burge and into the back of the net.
The Magpies celebrated, but the City fans stood to belt out a rendition of 'Play Up Sky Blues!', as the game restarted. County were now on the front foot, but City were having the best of the chances. Bayliss again came close to blowing the roof off the arena when he left-footed effort almost crept inside Collin's near post.
The introduction of Jordan Ponticelli with twenty minutes to go allowed the Sky Blues to go with three in attack, and City were rewarded with four minutes to go with a chance to draw level from the spot. Bayliss was heading away from goal when he was tripped by Matt Tootle, allowing McNulty to blast City level and send the stadium int the stratosphere.
Goals: Forte (51'), McNulty (87')
Yellows: Stokes (24'), Doyle (27'), Grant (73'), Hyam (74').
Coventry City XI: Burge (GK), Grimmer, Hyam, Davies, Stokes, Bayliss, Kelly, Doyle (C), Shipley (Ponticelli [70']), McNulty, Biamou (Clarke-Harris [82']).
Subs: O'Brien (GK), Willis, McDonald, Maguire-Drew, Reid.
Notts County XI: Collin (GK), Tootle, Hewitt, Duffy (C), Virtue, Grant, Forte (Smith [90']), Brisley, Noble (O'Connor [78']), Jones, Stead.
Subs: Fitzsimons (GK), Alessandra, Ameobi, Milsom, Hall.