Louis Reed’s superb free kick opened the scoring on 66 minutes before an equally brilliant effort from Lewis Wing restored parity.
In the closing stages, the Glovers threw everything at getting a winner they most definitely deserved but as they threw bodies forward, they were vulnerable to a counter and Dennis finished into an empty net with Artur Krysiak stranded.
Otis Khan was sent off for his frustrations.
Darren Way was forced into one change from the side that drew at Port Vale seven days ago.
Bevis Mugabi slotted in at centre-back in place of Omar Sowunmi, who was missing on medical grounds.
Another absentee was Southampton loanee Marcus Barnes. The young forward has been ruled out of action for six weeks with an ankle ligament injury.
His unfortunate exclusion left Francois Zoko and Sam Surridge as the only striker in the Town’s squad to lead their attacking cause.
However, the forward-thinking Khan was a menace from the off with his purposeful running and trickery.
The ex-Sheffield United man was the provider of the game’s first chance; his whipped free kick finding the head of Mugabi who nodded goalwards and central defensive partner Nathan Smith couldn’t quite get his foot on the ball to hook home from six yards.
Everything positive in the match came from Yeovil as Zoko twisted and turned his way into space to send a tame effort at Aaron Ramsdale and Jordan Green showed off his electric pace before seeing his shot blocked by Laurence Maguire.
Jared Bird was next to chance his arm but dragged his long-ranger wide and another of Khan’s mazy jaunts downfield ended with Ramsdale saving low to his left.
A badly judged header from Tom James allowed Chesterfield’s Chris O’Grady a rare sight on goal – Krysiak equal to his attempt to the near post – as the half began to peter out.
Zoko went close to bringing the crowd to their feet minutes prior to the interval. It would have been a goal of the season contender if his spectacular first-time volley had flown into the top corner instead of just over the crossbar.
Early in the second period, a Surridge header had the same result as he put James’ delicious delivery into the Thatchers terrace.
The AFC Bournemouth youngster would have had a glorious opportunity to put Town 1-0 if not for Maguire directing the ball out for a corner with the faintest of touches, and Mugabi was similarly inches away from a goal, a little nick off a blue shirt diverting it away from the Londoner.
Yeovil looked threatening every time they ventured into Chesterfield’s final third and when Ryan Dickson’s weaving dribble finished at the feet of Zoko, the Ivorian was unlucky to see his attempt bobbled marginally past the post.
The Glovers huffed and puffed for an opener but were dealt a killer blow when Reed fired the Spireites completely against the run of play.
The holding midfielder stepped up to take a free kick 20 yards from goal and sent a lovely dipper into the bottom corner past Krysiak’s despairing dive.
Immediately after conceding, the hosts were back on the front foot and Jake Gray’s piledriver went desperately close to creeping in.
Then a moment of brilliance levelled things up. Wing received possession 25 yards out and produced a stunner. Taking a touch out of his feet, the Middlesbrough attacked curled excellently over Ramsdale for his first senior goal in the EFL.
Khan stung the opposition stopper’s palms with a low strike seconds following the restart and James’ knuckleball set-piece needed to be clawed out of the top corner.
Way’s men penned Chesterfield deep into their half for the final few minutes, James skipping a shot just wide but a late blow was landed by the visitors with Dennis slotting into an empty net and Khan being sent off for venting his frustration at the referee.
Yeovil Town: Krysiak, James, Mugabi, N.Smith, Dickson, Green (C.Smith 76), Bird (Wing 69), Gray, Khan, Zoko, Surridge.
Sendings off: Khan 90.
Not used: Maddison, Whelan, Santos.
Chesterfield: Ramsdale, Whitmore, Nelson, Maguire, Weir, Reed, McCourt, Kay, Hines (Kellett 58), O’Grady (Dennis 84), Rowley.
Bookings: McCourt 20, Kay 74, Maguire 84
Not Used: Parkin, De Girolamo, Binnom-Williams, Wiseman, Dimaio.