Manager Ian Bogie made the expected changes with Chris Swailes swapping with Carl Jones, Martin Brittain for Harwood and Steven Richardson swapping with Darren Forsyth.
Despite more possession Gateshead couldn't break down the Tamworth defence and a defensive error by James Curtis allowed Nick Wright to put one past Jim Provett, who was left stranded, on 42 minutes.
Half Time: Gateshead 0, Tamworth 1.
As the second half ticked on, so did Bogie's mind. Thinking of a way to go forward and snatch a point.
A double substitution saw the side change formation from the conventional 4-4-2 to an unfamilier 4-3-3. Brittain and Wayne Phillips were off, Alex Francis and Darren Forsyth were on.
The change appeared to be working as Danny Alcock finally had to make saves from Forsyth and Mackay, while Francis lashed one over the crossbar.
Another daring move by Bogie was made, when right back Craig Baxter (who missed just seven minutes of football last season) was replaced by right winger Harwood.
The battle cry was sounded and four minutes from time Harwood delivered a blow to Tamworth.
A long throw by left back Mark Robinson entered the crowded penalty area, and it was Harwood who stabbed the ball home.
Gateshead now have to prepare for a daunting trip to Crawley, who beat Cambridge United 1-0.
Full Time: Gateshead 1, Tamworth 1.
Gateshead Line-up: Provett, Baxter, Robinson, Curtis, Swailes, Brittain, Phillips, Gate, Turnbull, Mackay, Richardson.
Subs: Farman, Francis (on for Brittain), Forsyth (on for Phillips), Harwood (on for Baxter), Jones.