His side fell to goals from Marios Ogkmpoe, who back-heeled home after an early corner, and David Templeton, who capitalised on a mix-up in the Motherwell midfield to net midway through the second half.
The 1,700 away fans were mostly long gone by the time substitute Gael Bigirimana gave Hamilton goalkeeper Gary Woods his first serious test of the game with a curling strike in stoppage-time.
Robinson said: “It was especially disappointing for the number of fans that turned up in the pouring rain. I think three-quarters of them left before the end and I wanted to join them to be honest with you.
“But that’s not the team we have come to know, that’s not the team the fans have come to know. We will have them back on Tuesday morning remembering what has got us our relative success this season.
“They have been well reminded after the game, I can assure you of that. We are a team that wins second balls and plays on the front foot.
“All of a sudden when you think you are better than what you are, football has a funny way of kicking you in the teeth, and that’s what happened.”
Robinson added: “We were chasing the game right from the start. We gave away a sloppy goal from a set-play that we warned them about. Their delivery from set-plays all day was better than ours.
“I don’t think we made their keeper make a save until the 93rd minute which probably summed up our threat.”
Hamilton manager Martin Canning was delighted for Ogkmpoe after the striker netted his first goal since his January move from Crete.
“He works his socks off, he’s such an honest, big guy,” said Canning after his side moved eight points off the bottom of the Ladbrokes Premiership.
“Him and Antonio Rojano give us a lot up front, they give us energy, they are physical, they can take it in.
“It’s important you get your reward for that as a striker. Yeah, you feel great when the team wins and when you have run about and worked hard, but when you get that goal it gives you that extra wee shot.”
Ogkmpoe showed some smart thinking to net from an 11th-minute corner for Hamilton.
The striker had his back to goal but did well to scoop the ball towards goal with his heel and Motherwell wing-back Richard Tait could only head it into the roof of the net.
Accies’ three-man defence were comfortable enough for the rest of the half. Tait and Curtis Main had strikes at goal but not from areas which were likely to succeed and the latter headed over from a difficult chance.
Robinson made a double switch in the 56th minute as Nadir Ciftci and Gael Bigirimana came on but Hamilton sealed the win when the visitors were caught out after a mix-up just inside their own half. Templeton stole possession before driving to the edge of the box and slotting into the far corner.