Shaun Gale was left to rue his side's set-piece shortcomings after the Hawks' 4-2 loss at local rivals Eastleigh.
Gale's men were on course for three Blue Square South points when they went into the break 2-1 up over the Spitfires.
But after the break, the Hawks' failed to heed Gale's pre-match warning of Eastleigh's set-piece strengths as three goals in the final 20 minutes left the visitors empty-handed.
'The story really is, if you don't defend set-pieces, you don't win games,' said Hawks boss Gale.
'We know Eastleigh are good at set pieces; they've got some strong, powerful players and their goals have come from that.
'We gave them three goals and you don't win football matches if you do that.
'I'm frustrated and massively disappointed for the lads because they put in a decent shift and they deserved more.'
After a cagey opening from both sides, it was the hosts who took the lead in the derby when Brett Williams capitalised on a lapse in concentration in the Hawks' back line to slot past keeper Aaron Howe.
That got the Hawks into action and they struck back six minutes from the break when Leon Cashman chipped a superb through ball from Guiseppe Sole back over Spitfires keeper Gareth Barfoot from the narrowest of angles.
And the away side surged ahead five minutes after that when Bobby Hopkinson's cross dropped in front of Sole, whose shot from the back of the box was slammed past Barfoot by Mustafa Tiryaki.
The half-time interval proved the turning point, though, when key man Tiryaki failed to reappear after suffering from a dead leg.
He was replaced by Hawks Academy graduate Liam Sewell.
But with the star striker out, Eastleigh regained the momentum.
It was former Hawk Tom Jordan who levelled the scores in the 72nd minute when he got on the end of a long free-kick from Williams and nestled a perfect header inside the top corner.
The Hawks thought they had retaken the lead two minutes from time when Wes Fogden's run into the box left Manny Williams to fire home but the goal was ruled out for offside.
Then calamity struck late on when Tony Taggart's corner was cleared only as far as the edge of the box and Williams was left in acres of space to net an easy header.
Eastleigh's win was sealed in injury-time as the referee's assistant penalised Jon McDonald for a debatable foul in the box on Williams, enabling Jamie Slabber – another ex-Hawk – to convert from the spot.
A frustrated Gale said: 'Losing Mustafa at half-time was a massive blow to us.
'If you look at our bench there was no strength or depth, especially compared to what Eastleigh can bring on.
'No disrespect to Liam (Sewell) but he's nave and young and Tiryaki's a big, strong player which we needed in a game like this. But that isn't an excuse because we came here to win and we gave a good account with a weakened side.
'I thought we deserved to get a lot more out of the game but that's football.
'We'll play a lot worse and win. Eastleigh haven't beaten us too often but this was their day.'