A blistering Ospreys first-half blew the visitors away, and despite improvement after the interval, Hammett's side could not overturn the deficit and slipped to a 26-15 loss.
The result leaves Blues tenth in the GUINNESS PRO12 table with just one win and one draw from their six games so far this campaign.
But Hammett was full of praise for the Ospreys and despite stepping it up after half-time knows his team must improve if they are to make any impact at all in Europe later this week.
"I thought the Ospreys played very well," he said. "Territory-wise, they battered us. Their fly-half and full-back kicked for position well.
"They had 67 per cent territory in that first half. It's very hard to play from that perspective.
"It was disappointing for us, but I have got to pay credit to the Ospreys. I thought some of their set-piece play was good.
"We didn't do ourselves a lot of favours in the tackle. Sometimes we were overloaded a bit in midfield and that opened up the Ospreys' width game.
"They played the pattern well, but certainly in the first half I thought we probably let them.
"Some of it was very good from them and some of it was average from us. We will look through it and be
honest going forwards.
"In the second half, we were obviously a lot better but we left it way too late. While we did get some shape and put some good pressure on them in the last 20 minutes, the Ospreys had the game won."
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