The two sides also played out a couple of draws during the regular season, but something has to give when they face off in the return leg at Meadow Lane next Friday.
Despite the wet conditions, Jack Grimmer played a nice one-two early on but was denied by a smart block, and the crossbar came to County's rescue soon after as McNulty's shot had a little too much on it.
Forte then made too much contact with his headed chance and Daniel Jones sent a shot-cross fizzing past the post in an end-to-end first half.
Lee Burge stuck out a leg to keep out the lively Forte, as County went in search of a third win at this ground in five visits.
Coventry thought that they had netted before half time, but Adam Collin stopped the ball on the line and the goal-line technology confirmed that it had not crossed over.
A goal seemed inevitable and it went the visitors' way when it arrived four minutes into the second half after Forte turned the ball over the line with a backheeled shot.
Jorge Grant saw a shot from 25 yards kept out and Bayliss almost found a way through from a tight angle as both sides went in search of the game's second goal.
That goal would arrive late on in the contest through the successfully converted McNulty pen, profiting from Matt Tootle's tackle on Bayliss, although replays suggest that Gavin Ward was perhaps wrong to point to the spot.
A chance went begging for Tom Davies to win it for the Sky Blues right at the death, leaving the match in the balance ahead of the return leg.
COVENTRY CITY (4-4-2): Burge; Grimmer, Hyam, Davies, Stokes; Bayliss, Doyle, Kelly, Shipley (Ponticelli 72'); McNulty, Biamou (Clarke-Harris 83')
NOTTS COUNTY (4-2-2-2): Collin; Tootle, Duffy, Brisley, Jones; Hewitt, Noble (O'Connor 77') Virtue-Thick (Alessandra 58'), Grant; Stead, Forte (Smith 96')