The Harriers were beaten 2-0 at high-flying Brackley Town - watch match highlights here - having beaten Alfreton Town just two days earlier.
Lee Ndlovu puts the hosts in front in the first-half and then James Armson struck in the second period to take Brackley's point total to 19.
For Harriers, they slipped to their fourth defeat of the season and have picked up nine points from seven games.
They were without key players Joel Taylor, Joe Ironside and Dan Bradley but Eustace wasn't going to blame their defeat on that.
"That’s no excuse – the eleven I picked all want to play in the team and all come to me and say ‘why aren’t I playing?" he told the club's website.
"There’s no excuse at all – we picked a strong team and we’re disappointed with the result. It was better in the second half but we didn’t get the ball in the box enough and didn’t have enough.
“We conceded such a sloppy second goal and it knocked the wind out of us a bit. It’s not good enough.”
Eustace issues a message for the Kiddy fans, saying: "I know it is tough at the moment.
“They’ve got behind us ever since I’ve come in; they’ve been fantastic and that’s what’s so disappointing.
“We haven’t been performing as we should be and I apologise to those fans but we are working hard to get it right.”